tst_QCompleter::QTBUG_51889_activateSendTwice remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Id670b3f3cf34438c729afc3c82faf18a45b45d4f
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/util/qcompleter/tst_qcompleter.cpp

@@ -1786,7 +1786,6 @@ void tst_QCompleter::QTBUG_51889_activatedSentTwice()
     const auto pos = w.screen()->availableGeometry().topLeft() + QPoint(200,200);
     w.move(pos);
     w.show();
-    QApplicationPrivate::setActiveWindow(&w);
     QVERIFY(QTest::qWaitForWindowActive(&w));
 
     QSignalSpy activatedSpy(&cbox, &QComboBox::activated);