bos: Remove last of MRAFS references

A few MRAFS tidbits were left behind during the cleanup in commit
a9301cd2dc1a875337f04751e38bba6f1da7ed32.

Change-Id: I7dcd30797ff87c61d57781c66cb9f7369638fa36
Reviewed-on: http://gerrit.openafs.org/10808
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>