tst_QGraphicsScene::taskQTBUG_16401_focusItem remove setActiveWindow()

2f6fe3a268 has made calls to
QApplicationPrivate::setActiveWindow() redundant.

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I65999d64a67309fd3a3b785e7aaa508a8c6caebb
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/graphicsview/qgraphicsscene/tst_qgraphicsscene.cpp

@@ -4911,7 +4911,6 @@ void tst_QGraphicsScene::taskQTBUG_16401_focusItem()
     rect->setFlag(QGraphicsItem::ItemIsFocusable);
 
     view.show();
-    QApplicationPrivate::setActiveWindow(&view);
     QVERIFY(QTest::qWaitForWindowActive(&view));
 
     QVERIFY(!scene.focusItem());