staging: comedi: remove "comedi_fc.h"

None of the comedi low-level drivers include "comedi_fc.h" any longer,
so remove it.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>