media: lirc: remove unused feature LIRC_CAN_SET_REC_DUTY_CYCLE

There is no hardware which can filter input on the duty cycle, so no
driver implements this. On top of that, LIRC_CAN_SET_REC_DUTY_CYCLE
has the same value as LIRC_CAN_MEASURE_CARRIER (0x02000000).

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>