staging: comedi: dt3000: remove proc subdevice

This subdevice is not allocated or defined in the driver. Remove the
disabled subdevice initialization.

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>