afsmonitor: Use roken

Include the roken.h header, and remove the redundant system
includes from afsmonitor.c

Change-Id: Ia3eb8a7a0bb1e77d928d26cdfc87f818e6791e16
Reviewed-on: http://gerrit.openafs.org/9463
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>