[media] lirc: delete unused init/exit function prototypes

The lirc sasem and imon drivers now use the module_usb_driver macro, so the old
init/exit function prototypes are useless.

This patch eliminates this warnings:

media_build/v4l/lirc_imon.c:74:19: warning: 'imon_init' declared 'static' but never defined [-Wunused-function]
media_build/v4l/lirc_imon.c:75:20: warning: 'imon_exit' declared 'static' but never defined [-Wunused-function]
media_build/v4l/lirc_sasem.c:84:19: warning: 'sasem_init' declared 'static' but never defined [-Wunused-function]
media_build/v4l/lirc_sasem.c:85:20: warning: 'sasem_exit' declared 'static' but never defined [-Wunused-function]

Signed-off-by: Gianluca Gennari <gennarone@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>