tst_QButtonGroup::arrowKeyNavigation() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Icd8737a881712bb9192b401a0e318fcec4622ac2
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/widgets/qbuttongroup/tst_qbuttongroup.cpp

@@ -122,7 +122,6 @@ void tst_QButtonGroup::arrowKeyNavigation()
     layout.addWidget(&g2);
 
     dlg.show();
-    QApplicationPrivate::setActiveWindow(&dlg);
     QVERIFY(QTest::qWaitForWindowActive(&dlg));
 
     bt1.setFocus();