[media] lirc_dev: remove pointless functions

drv->set_use_inc and drv->set_use_dec are already optional so we can
remove all dummy functions.

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>