ubik: Remove 'mtime' from ubik_stat

ubik: Remove 'mtime' from ubik_stat

Nothing uses the 'mtime' field from ubik_stat. Remove it.

Reviewed-on: https://gerrit.openafs.org/13068
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit b8617f08d1bf57a6b3fbba44e5b4de24dc84a9bb)

Change-Id: I1770e55aa45192b4bab6d4256be562cb308fd03a
Reviewed-on: https://gerrit.openafs.org/13118
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>