forcing Qt native paint system is not necessary anymore

bf4b61c7b7f2ca1d9641ab0cf5f88a68bc3930d0 fixed the problem.

vcl/unx/kde4/KDEXLib.cxx

@@ -168,9 +168,6 @@ void KDEXLib::Init()
 
     KCmdLineArgs::init( m_nFakeCmdLineArgs, m_pAppCmdLineArgs, kAboutData );
 
-#if QT_VERSION >= QT_VERSION_CHECK( 4, 5, 0 )
-    QApplication::setGraphicsSystem( "native" ); // fdo#30991
-#endif
     m_pApplication = new VCLKDEApplication();
     kapp->disableSessionManagement();
     KApplication::setQuitOnLastWindowClosed(false);