[media] nuvoton-cir: carrier detect support is broken - remove it

The carrier detect return value is never used on nuvoton driver:
drivers/media/rc/nuvoton-cir.c: In function 'nvt_process_rx_ir_data':
drivers/media/rc/nuvoton-cir.c:623:6: warning: variable 'carrier' set but not used [-Wunused-but-set-variable]
Also, this would be called only if a boolean variable is enabled,
but there's no condition that enables it inside the driver. So,
comment the carrier detection code, as it might be useful later,
and remove the unused glue code.

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