[media] ov7670: remove legacy ctrl callbacks

via-camera and mcam-core were the only bridge drivers that used ov7670.
Since now they have been moved to use the ctrl framework, the old
legacy callbacks in the ov7670 can be removed.

Signed-off-by: Javier Martin <javier.martin@vista-silicon.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>