[media] ds3000: remove ts2020 tuner related code

remove ts2020 tuner related code from ds3000 driver
prepare ds3000 driver for using external tuner driver

Signed-off-by: Konstantin Dimitrov <kosio.dimitrov@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>