staging: comedi: comedi.h: remove struct comedi_trig

Remove `struct comedi_trig` and some associated macros, `TRIG_DITHER`,
`TRIG_DEGLITCH`, `TRIG_CONFIG`, and ioctl code `COMEDI_TRIG`.  These
have been obsolete since COMEDI release 0.7.61 back in November 2001.

The userspace COMEDILIB library still has some deprecated code that
may attempt to use these, but it uses its own, compatible version of
"comedi.h", so isn't affected by their removal from the kernel copy.

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