[media] bttv: remove unneeded locking comments

After Mauro's "bttv: Fix locking issues due to BKL removal code" there
are a number of comments that are no longer needed about lock ordering.
Remove them.

Signed-off-by: Brandon Philips <bphilips@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>