delete all associated code soon; since the maxcsn will be updated as
soon as any write op occurs, it's no big deal for this to be out of date.
Also, since the maxcsn will get checkpointed on close, it will only get
out of date on an actual slapd crash, which is hopefully too rare to
worry about.

re-fetch the request; since the mutex has been released wile freeing the message, it may have been already removed by someone else (ITS#3800)