tst_QItemDelegate::decoration() remove setActiveWindow()

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

Remove redundant calls.

Task-number: QTBUG-121488
Change-Id: If9058e015fa8223c3c318ba240eddf2ab24949be
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

tests/auto/widgets/itemviews/qitemdelegate/tst_qitemdelegate.cpp

@@ -1025,7 +1025,6 @@ void tst_QItemDelegate::decoration()
     TestItemDelegate delegate;
     table.setItemDelegate(&delegate);
     table.show();
-    QApplicationPrivate::setActiveWindow(&table);
     QVERIFY(QTest::qWaitForWindowActive(&table));
 
     QVariant value;