PYCBC-141: Remove duplicate mention of 'add'

Change-Id: I108d959fb1a8ec3a7881fd63285b07abaf45ebd1
Reviewed-on: http://review.couchbase.org/27085
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>