Remove Q_DEAD_CODE_FROM_QT4_MAC section

Its not known if the call to flush() is required in
Qt 5. It has been compiled out until now; remove it.

Change-Id: I7033e02af8ac7ea2a357d1287e368b541d1d6776
Reviewed-by: Timur Pocheptsov <Timur.Pocheptsov@digia.com>

src/widgets/dialogs/qprogressdialog.cpp

@@ -697,9 +697,6 @@ void QProgressDialog::setValue(int progress)
                 d->shown_once = true;
             }
         }
-#ifdef Q_DEAD_CODE_FROM_QT4_MAC
-        QApplication::flush();
-#endif
     }
 
     if (progress == d->bar->maximum() && d->autoReset)