tst_QWidget::tabOrderWithProxyDisabled() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I88d39def0e85e147b3621d98d150ee65463be94f
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

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

@@ -2357,7 +2357,6 @@ void tst_QWidget::tabOrderWithProxyDisabled()
     container.show();
     container.activateWindow();
 
-    QApplicationPrivate::setActiveWindow(&container);
     if (!QTest::qWaitForWindowActive(&container))
         QSKIP("Window failed to activate, skipping test");