Revert "Add workaround for QTBUG-35143"

It was just a shortterm hack for RC1
This reverts commit e4d800ad4a.

Change-Id: If4471a8e040c7f9517551914b092b7ad0cd6d1d7
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/app/main.cpp

@@ -298,7 +298,6 @@ int main(int argc, char **argv)
 #if defined(Q_OS_UNIX) && !defined(Q_OS_MAC)
     // QML is unusable with the xlib backend
     QApplication::setGraphicsSystem(QLatin1String("raster"));
-    qputenv("QSG_RENDER_LOOP", "basic"); // workaround for QTBUG-35143
 #endif
 
     SharedTools::QtSingleApplication app((QLatin1String(appNameC)), argc, argv);