tst_QGraphicsProxyWidget::tabFocus_simpleWidget remove setActiveWindow

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I5dacd3971305e33a6d1314b798d4211425b68d68
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

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

@@ -1538,7 +1538,6 @@ void tst_QGraphicsProxyWidget::tabFocus_simpleWidget()
     window.setLayout(layout);
 
     window.show();
-    QApplicationPrivate::setActiveWindow(&window);
     window.activateWindow();
     QVERIFY(QTest::qWaitForWindowActive(&window));