TabFocus_sceneWithFocusableItems() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Iacc45c6bad54c4356e7db1c489897a2a74d2936a
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

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

@@ -3095,7 +3095,6 @@ void tst_QGraphicsScene::tabFocus_sceneWithFocusableItems()
     widget.setWindowTitle(QTest::currentTestFunction());
     widget.setLayout(layout);
     widget.show();
-    QApplicationPrivate::setActiveWindow(&widget);
     widget.activateWindow();
     QVERIFY(QTest::qWaitForWindowActive(&widget));