Revert "QWidgetWindow: call base class close event impl".

The patch causes the window creation on reshowing nested QWidget
with native windows to create child windows with 0-parent handles,
which can have adverse effects on the various platforms.
The patch might be re-applied on top of
73c86fcb.

This reverts commit 470c8b68

.

Task-number: QTBUG-43344
Task-number: QTBUG-50854
Change-Id: I2ad837c3800fc71cccf04d455d1b9c3600b233e7
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Reviewed-by: Andy Shaw <andy.shaw@theqtcompany.com>