Remove santa hat easter egg

It made a lot of stressed GIS people smile (and as a bonus
stressed out some unhappy grinches in the process!), but
there's nothing worse than a good easter egg which lives
on too long and gets tired.

RIP santa QGIS... bring on the next easter egg!

(cherry-picked from 12a4a9)

src/core/qgsapplication.cpp

@@ -396,7 +396,7 @@ QString QgsApplication::activeThemePath()
 
 QString QgsApplication::appIconPath()
 {
-  return iconsPath() + ( QDate::currentDate().month() == 12 ? tr( "qgis-icon-60x60_xmas.png", "December application icon" ) : QString( "qgis-icon-60x60.png" ) );
+  return QString( "qgis-icon-60x60.png" );
 }
 
 QString QgsApplication::iconPath( const QString& iconFile )