media: v4l2: Remove vidioc_g_ctrl callback

All the drivers either use the control framework or provide a
vidioc_g_ext_ctrls callback. We can remove this callback.

Thanks for your service!

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>