tst_QApplication::focusWidget() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I160e71302b40777d13e2481447bc47ebfc1a784c
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

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

@@ -1622,7 +1622,6 @@ void tst_QApplication::focusWidget()
         QTextEdit te;
         te.show();
 
-        QApplicationPrivate::setActiveWindow(&te);
         QVERIFY(QTest::qWaitForWindowActive(&te));
 
         const auto focusWidget = QApplication::focusWidget();