Linux 3.18: key_type no longer has a match op

Structure key_type no longer has a match op, and
overriding the default matching has to be done
differently.

Our current match op doesn't do anything special so there's
no need to try to override the defaults; just remove the
assignment of .match and the associated function.

Reviewed-on: http://gerrit.openafs.org/11563
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit b5de4a9f42bb83ae03f2f647b11a1200a502d013)

Change-Id: I7baca4a7f02eac45671e1e9ebf48534cdd5830be
Reviewed-on: http://gerrit.openafs.org/11570
Reviewed-by: Anders Kaseorg <andersk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>