dropped remains of old-style vbucket update tracking

Change-Id: I3ccb6bc492ac91e1a586f2c7a6ed9c54c7a863c6
Reviewed-on: http://review.couchbase.org/40087
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>