[media] adv7604: Remove deprecated video-level DV timings operations

The video enum_dv_timings and dv_timings_cap operations are deprecated
and unused. Remove them.

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