dell-laptop: Remove rfkill code

dell-laptop: Remove rfkill code

The interface just doesn't work on some machines, and Dell haven't been
able to tell us either which machines those are or what we should be
doing instead. This would be fine, except it results in userspace ending
up confused and general sadness. So let's just rip it out for now.

Signed-off-by: Matthew Garrett <mjg@redhat.com>