remove mc_couch related code

not needed anymore since couch notifier is removed from ep_engine

Change-Id: Id6f7cc228b36b63a9ccf83a8d97842c712d015ba
Reviewed-on: http://review.couchbase.org/41000
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>