tst_QApplication::focusWidget() remove setActiveWindow() child section

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Ib3b39f4bd51c87eeeebe329ada163f24390f6bc3
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/kernel/qapplication/tst_qapplication.cpp

@@ -1637,7 +1637,6 @@ void tst_QApplication::focusWidget()
         QTextEdit te(&w);
         w.show();
 
-        QApplicationPrivate::setActiveWindow(&w);
         QVERIFY(QTest::qWaitForWindowActive(&w));
 
         const auto focusWidget = QApplication::focusWidget();