staging: comedi: comedidev.h: remove unused "minor bits" information

The enum comedi_minor_bits and the COMEDI_SUBDEVICE_MINOR_{SHIFT,OFFSET}
defines are not used. Remove them.

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