Remove unused support for XMPP

Change-Id: I41664929a1ca8e72aedd31d305b45f39b4196458
Reviewed-on: http://review.couchbase.org/25980
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>