CBLT-159:  remove mentions of "stable" in comments

Change-Id: I3845e8414d4ed6c19e1f7170e206c615bae62e42
Reviewed-on: http://review.couchbase.org/37908
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>