tst_QCompleter::tast253125_linedEditCompletion remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Ie06a9326cb06f4ba657e065a52dfa1d8b319086b
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

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

@@ -1387,7 +1387,6 @@ void tst_QCompleter::task253125_lineEditCompletion()
     edit.move(200, 200);
     edit.show();
     edit.setFocus();
-    QApplicationPrivate::setActiveWindow(&edit);
     QVERIFY(QTest::qWaitForWindowActive(&edit));
 
     QTest::keyClick(&edit, 'i');