Remove layer/legend/palette preview from raster layer properties

These boxes were not very useful - two of them (legend and palette)
have been disabled for many years now, and the layer preview was
occasionally causing an exception when used with contour renderer,
which caused the raster properties dialog to fail to load at all.

See https://lists.osgeo.org/pipermail/qgis-developer/2020-November/062651.html

(cherry picked from commit b0f5f09)

src/gui/raster/qgsrasterlayerproperties.cpp

@@ -856,24 +856,6 @@ void QgsRasterLayerProperties::sync()
   mLayerOrigNameLineEd->setText( mRasterLayer->name() );
   leDisplayName->setText( mRasterLayer->name() );
 
-  //get the thumbnail for the layer
-  QPixmap thumbnail = QPixmap::fromImage( mRasterLayer->previewAsImage( pixmapThumbnail->size() ) );
-  pixmapThumbnail->setPixmap( thumbnail );
-
-  // TODO fix legend + palette pixmap
-
-  //update the legend pixmap on this dialog
-#if 0
-  pixmapLegend->setPixmap( mRasterLayer->legendAsPixmap() );
-  pixmapLegend->setScaledContents( true );
-  pixmapLegend->repaint();
-
-  //set the palette pixmap
-  pixmapPalette->setPixmap( mRasterLayer->paletteAsPixmap( mRasterLayer->bandNumber( mRasterLayer->grayBandName() ) ) );
-  pixmapPalette->setScaledContents( true );
-  pixmapPalette->repaint();
-#endif
-
   QgsDebugMsgLevel( QStringLiteral( "populate metadata tab" ), 2 );
   /*
    * Metadata Tab
@@ -1113,10 +1095,6 @@ void QgsRasterLayerProperties::apply()
 
   mRasterLayer->setCrs( mCrsSelector->crs() );
 
-  //get the thumbnail for the layer
-  QPixmap thumbnail = QPixmap::fromImage( mRasterLayer->previewAsImage( pixmapThumbnail->size() ) );
-  pixmapThumbnail->setPixmap( thumbnail );
-
   if ( mRasterLayer->shortName() != mLayerShortNameLineEdit->text() )
     mMetadataFilled = false;
   mRasterLayer->setShortName( mLayerShortNameLineEdit->text() );

src/ui/qgsrasterlayerpropertiesbase.ui

@@ -1243,129 +1243,6 @@ border-radius: 2px;</string>
                  </layout>
                 </widget>
                </item>
-               <item>
-                <layout class="QHBoxLayout" name="horizontalLayout_10">
-                 <item>
-                  <spacer name="spacer_2">
-                   <property name="orientation">
-                    <enum>Qt::Horizontal</enum>
-                   </property>
-                   <property name="sizeHint" stdset="0">
-                    <size>
-                     <width>0</width>
-                     <height>20</height>
-                    </size>
-                   </property>
-                  </spacer>
-                 </item>
-                 <item>
-                  <widget class="QGroupBox" name="groupBox10">
-                   <property name="title">
-                    <string>Thumbnail</string>
-                   </property>
-                   <layout class="QGridLayout" name="_7">
-                    <item row="0" column="0">
-                     <widget class="QLabel" name="pixmapThumbnail">
-                      <property name="minimumSize">
-                       <size>
-                        <width>120</width>
-                        <height>120</height>
-                       </size>
-                      </property>
-                      <property name="maximumSize">
-                       <size>
-                        <width>120</width>
-                        <height>120</height>
-                       </size>
-                      </property>
-                      <property name="frameShape">
-                       <enum>QFrame::StyledPanel</enum>
-                      </property>
-                      <property name="scaledContents">
-                       <bool>true</bool>
-                      </property>
-                     </widget>
-                    </item>
-                   </layout>
-                  </widget>
-                 </item>
-                 <item>
-                  <widget class="QGroupBox" name="groupBox9">
-                   <property name="title">
-                    <string>Legend</string>
-                   </property>
-                   <layout class="QGridLayout" name="_8">
-                    <item row="0" column="0">
-                     <widget class="QLabel" name="pixmapLegend">
-                      <property name="minimumSize">
-                       <size>
-                        <width>120</width>
-                        <height>120</height>
-                       </size>
-                      </property>
-                      <property name="maximumSize">
-                       <size>
-                        <width>120</width>
-                        <height>120</height>
-                       </size>
-                      </property>
-                      <property name="frameShape">
-                       <enum>QFrame::Box</enum>
-                      </property>
-                      <property name="scaledContents">
-                       <bool>true</bool>
-                      </property>
-                     </widget>
-                    </item>
-                   </layout>
-                  </widget>
-                 </item>
-                 <item>
-                  <widget class="QGroupBox" name="groupBox8">
-                   <property name="title">
-                    <string>Palette</string>
-                   </property>
-                   <layout class="QGridLayout" name="_9">
-                    <item row="0" column="0">
-                     <widget class="QLabel" name="pixmapPalette">
-                      <property name="minimumSize">
-                       <size>
-                        <width>120</width>
-                        <height>120</height>
-                       </size>
-                      </property>
-                      <property name="maximumSize">
-                       <size>
-                        <width>120</width>
-                        <height>120</height>
-                       </size>
-                      </property>
-                      <property name="frameShape">
-                       <enum>QFrame::Box</enum>
-                      </property>
-                      <property name="scaledContents">
-                       <bool>true</bool>
-                      </property>
-                     </widget>
-                    </item>
-                   </layout>
-                  </widget>
-                 </item>
-                 <item>
-                  <spacer name="spacer">
-                   <property name="orientation">
-                    <enum>Qt::Horizontal</enum>
-                   </property>
-                   <property name="sizeHint" stdset="0">
-                    <size>
-                     <width>0</width>
-                     <height>20</height>
-                    </size>
-                   </property>
-                  </spacer>
-                 </item>
-                </layout>
-               </item>
                <item>
                 <spacer name="verticalSpacer">
                  <property name="orientation">