tst_QGraphicsSceneIndex::clear() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Ied2110ec9d1f7695bee2589ce4f3055ea8a78615
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/graphicsview/qgraphicssceneindex/tst_qgraphicssceneindex.cpp

@@ -322,7 +322,6 @@ void tst_QGraphicsSceneIndex::clear()
 
     QGraphicsView view(&scene);
     view.show();
-    QApplicationPrivate::setActiveWindow(&view);
     QVERIFY(QTest::qWaitForWindowActive(&view));
     scene.clear();