Remove unneeded inclusion of <sys/timeb.h>

This file is deprecated on FreeBSD, and is not used anywhere.

Change-Id: If10816f26da91855d10826d53501e5b9974cd292
Reviewed-on: http://gerrit.openafs.org/10817
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>