dmxDestroyWindow() - must call the X's native DetroyWindow()

Don't really know why this section was disabled, but without it,
certain pPicture resources do not get free'd until later in the
FreeClientResources() process after the screen has been free'd -
resulting in seg fault.

With this patch, all resources normally free'd using vanilla X are
now also being freed correctly by Xdmx.

https://bugs.freedesktop.org/show_bug.cgi?id=24576



Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>