[media] rc-core: remove generic scancode filter

The generic scancode filtering has questionable value and makes it
impossible to determine from userspace if there is an actual
scancode hw filter present or not.

So revert the generic parts.

Based on a patch from James Hogan <james.hogan@imgtec.com>, but this
version also makes sure that only the valid sysfs files are created
in the first place.

Signed-off-by: David Härdeman <david@hardeman.nu>
Acked-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>