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
73c86fcb40.

This reverts commit 470c8b68df.

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>

src/widgets/kernel/qwidgetwindow.cpp

@@ -708,7 +708,6 @@ void QWidgetWindow::handleCloseEvent(QCloseEvent *event)
 {
     bool is_closing = m_widget->d_func()->close_helper(QWidgetPrivate::CloseWithSpontaneousEvent);
     event->setAccepted(is_closing);
-    QWindow::event(event); // Call QWindow QCloseEvent handler.
 }
 
 #ifndef QT_NO_WHEELEVENT