V4L/DVB (8678): Remove the dead CONFIG_RADIO_MIROPCM20{,_RDS} code

The CONFIG_RADIO_MIROPCM20{,_RDS} code became dead code 1.5 years ago.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>