MB-11235 rename "UPR replication backlog" to "Intra-Replication Queue"

.. by request from Perry Krug

Change-Id: I38a8a9a22ffde728e0b617b74f42c9f3264f3bef
Reviewed-on: http://review.couchbase.org/38980
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>