[media] tda6655: get rid of get_state()/set_state()

Those ops aren't used by any driver, with is weird. I suspect
that mantis_vb3030 driver were not working properly...

Anyway, now that the driver uses the set_parms, the DVB
frontend core should do the right thing.

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