Staging: comedi: remove RT code

This removes the unused RT code from the comedi subsystem.

A lot of drivers needed to then include interrupt.h on their own, as they
were picking it up through the comedi_rt.h inclusion.

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>