tst_QButtonGroup::task106609() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: I8cd3ce928ede88ad7351174f6d34c29ba0a7e246
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/widgets/qbuttongroup/tst_qbuttongroup.cpp

@@ -433,7 +433,6 @@ void tst_QButtonGroup::task106609()
     qRegisterMetaType<QAbstractButton*>("QAbstractButton*");
     QSignalSpy spy1(buttons, SIGNAL(buttonClicked(QAbstractButton*)));
 
-    QApplicationPrivate::setActiveWindow(&dlg);
     QTRY_COMPARE(QApplication::activeWindow(), static_cast<QWidget*>(&dlg));
 
     radio1->setFocus();