tabFocus_complexTwoWidgets() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I60c873e4df7f5183bd1a9f295f6e916d224b6794
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/graphicsview/qgraphicsproxywidget/tst_qgraphicsproxywidget.cpp

@@ -1889,7 +1889,6 @@ void tst_QGraphicsProxyWidget::tabFocus_complexTwoWidgets()
     window.setLayout(layout);
 
     window.show();
-    QApplicationPrivate::setActiveWindow(&window);
     window.activateWindow();
     QVERIFY(QTest::qWaitForWindowActive(&window));