[media] dvb: remove the track() fops

[media] dvb: remove the track() fops

This callback is not used anywhere. Maybe it were used in the
past to optimize the custom algo, but, as it is not used anymore,
let's just remove it.

If later needed, some patch may re-add it with a proper
implementation.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>