Removed getReplicaMulti from documentation.

The function no longer exists in the extension itself.

Change-Id: I63ebfb7357d74fbf31154944897a463245a224e2
Reviewed-on: http://review.couchbase.org/29266
Tested-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>