staging: comedi: comedidev.h: remove unused callbacks from comedi_subdevice

The 'do_lock' and 'do_unlock' callbacks are not used be any of the comedi
drivers or the comedi core. Just 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>