removed ancient left-over test from tst_qwidget

removed ancient left-over test from tst_qwidget

The part of tst_qwidget::reparent() that "makes sense only on Windows"
is antiquated at least since the introduction of alien widgets.
It basically tests if QWidget::winId() returns a valid window handle
(has been replaced with winHandleOf here in the meantime).
This is always successful, because winId() creates a valid window handle.

Change-Id: I52c370e26fd9b34861bd4d52c12dded243382d43
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>