Remove unused help button from style manager (fix #14055)

(cherry-picked from 17ed9d1)

Author: nyalldawson

src/ui/qgsstylev2managerdialogbase.ui

@@ -398,7 +398,7 @@ QMenu::item:selected {  background-color: gray; } */
             <enum>Qt::Horizontal</enum>
            </property>
            <property name="standardButtons">
-            <set>QDialogButtonBox::Close|QDialogButtonBox::Help</set>
+            <set>QDialogButtonBox::Close</set>
            </property>
            <property name="centerButtons">
             <bool>false</bool>