media: Documentation: userspace-api: media: drop clipping, destructive overlays

Support for clipping for overlays has been removed, update the
documentation.

Support for destructive overlay support has been removed as well,
also update the documentation for this.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>