tst_QComboBox::keyBoardNavationWithMouse() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Iea8d365bb6e07663517aa710d4730e728d3d1533
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp

@@ -2794,7 +2794,6 @@ void tst_QComboBox::keyBoardNavigationWithMouse()
 
     combo.move(200, 200);
     combo.showNormal();
-    QApplicationPrivate::setActiveWindow(&combo);
     QVERIFY(QTest::qWaitForWindowActive(&combo));
 
     QCOMPARE(combo.currentText(), QLatin1String("0"));