tst_QCompleter::focusIn() remove QApplicationPrivate::setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I129183b6e65da297d457fbebfeba940daffc9b3d
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

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

@@ -1105,7 +1105,6 @@ void tst_QCompleter::focusIn()
     window.move(200, 200);
     window.show();
     window.activateWindow();
-    QApplicationPrivate::setActiveWindow(&window);
     QVERIFY(QTest::qWaitForWindowActive(&window));
 
     auto comboBox = new QComboBox(&window);