Fix memory leak when queueing messages in a PassiveStream

Upr mutations, deletions, and expirations contain and Item and we
need to make sure they get freed if a stream is dead.

Change-Id: I504b326e3af2ca5493df54c205feacaa9a97c9f5
Reviewed-on: http://review.couchbase.org/38333
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>