Removed QGstreamerVideoOverlay and related classes. It was used as
'Window' control but performs worse than QGstreamerVideoWindow which
does basically the same thing using GStreamer ready-made components
instead.
Removed X11 dependencies and related configuration tests. It was only
needed for QGstreamerVideoOverlay.
Change-Id: I2ad2636ccf0060e56cd64f3d9e5b3c24dc75f5a3
Reviewed-by: Andy Nichols <andy.nichols@digia.com>