staging: comedi: comedi_fops: remove disabled subdevice lock/unlock callback

According to Ian Abbott, this code was added in comedi-0.7.6 back in June 1999
and has always been disabled.

The 'lock_f' and 'unlock' members don't even exist in the comedi_subdevice.
Just remove the disabled code.

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>