V4L/DVB (11365): tvaudio: remove i2c legacy code

All drivers that use tvaudio now use v4l2_subdev, so we can remove the
legacy code from tvaudio.

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