[media] v4l2-subdev: drop get/set_crop pad ops

Drop the duplicate get/set_crop pad ops and only use get/set_selection.
It makes no sense to have two duplicate ops in the internal subdev API.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>