Remove unused functionality in AtomicQueue

Change-Id: Ic18d74484ed89d1d7e0debc7f007c38946c2b9a5
Reviewed-on: http://review.couchbase.org/31329
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>