V4L/DVB (11283): saa6588: remove legacy code.

saa6588 is now only used through v4l2_subdev, so we can remove the old legacy
code.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>