tst_QStackedWidget::dynamicPages() remove setActiveWindow()

2f6fe3a26843ff68c5d3f9af0a2fc3cce6caac22 as made calls to
QApplicationPrivate::setActiveWindow() redundant.

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: If6d2bbde186d21662bf9a72b0b03152317724f01
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/widgets/qstackedwidget/tst_qstackedwidget.cpp

@@ -159,7 +159,6 @@ void tst_QStackedWidget::dynamicPages()
     le11->setFocus();   // set focus to second widget in the page
     sw->resize(200, 200);
     sw->show();
-    QApplicationPrivate::setActiveWindow(sw);
     QVERIFY(QTest::qWaitForWindowActive(sw));
     QTRY_COMPARE(QApplication::focusWidget(), le11);