[media] cx25821: remove custom ioctls that duplicate v4l2 ioctls

No idea why these custom ioctls exist: they have perfectly normal v4l2
counterparts which are already implemented.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>