staging: comedi: remove unused 'channel flags' support

The `flags` and `flaglist` members of `struct comedi_subdevice` were
defined to supply "all-channel" flags via the `COMEDI_SUBDINFO` ioctl,
or "channel-specific" flags via the `COMEDI_CHANINFO` ioctls,
respectively.  However, no comedi driver has ever set them.

It's not entirely clear how "all-channel" flags would differ from the
"subdevice" flags passed by `COMEDI_SUBDINFO`.  It is conceivable that
"channel-specific" flags could be used to describe different analog
reference values (or whatever) supported by different channels.
Presumably these would use some sub-set of the `SDF_xxx` subdevice flag
values, or possibly the `CR_xxx` flag values that get packed into a
"chanspec" value (along with a channel number and range code).  The
original intentions are lost in the mists of time.

For now, just remove the `flags` and `flaglist` members from `struct
comedi_subdevice` and behave as though they have been left at their
default values (0 or NULL) by the low-level comedi driver.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>