V4L/DVB: dvb-usb: get rid of struct dvb_usb_rc_key

dvb-usb has its own IR handle code. Now that we have a Remote
Controller subsystem, we should start using it. So, remove this
struct, in favor of the similar struct defined at the RC subsystem.

This is a big, but trivial patch. It is a 3 line delect, plus
lots of rename on several dvb-usb files.

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