tst_QFileDialog2::QTBUG6558_showDirsOnly() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: Ief817a31685e23af57fdcc0909c6e605072d83fd
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/dialogs/qfiledialog2/tst_qfiledialog2.cpp

@@ -1265,7 +1265,6 @@ void tst_QFileDialog2::QTBUG6558_showDirsOnly()
     fd.setOption(QFileDialog::ShowDirsOnly, true);
     fd.show();
 
-    QApplicationPrivate::setActiveWindow(&fd);
     QVERIFY(QTest::qWaitForWindowActive(&fd));
     QCOMPARE(fd.isVisible(), true);
     QCOMPARE(QApplication::activeWindow(), static_cast<QWidget*>(&fd));