Remove kauth headers from afs_usrops.c

Since ka_* functions are no longer called from here, we don't need
the headers

Change-Id: I538c27cf4fe2f16811d1d3056b25054c80ba5b2a
Reviewed-on: http://gerrit.openafs.org/9956
Reviewed-by: D Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>