tst_QWidget::tabOrderWithProxyOutOfOrder() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I7a4b21018216c2b7cced8d4aa5084c527b694f4a
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -2529,7 +2529,6 @@ void tst_QWidget::tabOrderWithProxyOutOfOrder()
 
     container.show();
     container.activateWindow();
-    QApplicationPrivate::setActiveWindow(&container);
     if (!QTest::qWaitForWindowActive(&container))
         QSKIP("Window failed to activate, skipping test");