dropped janitor_agent:apply_new_bucket_config/5

It's clearest to have single point of entry

Change-Id: I35bf5de48d85c824697fabd2fa4d5fc827193181
Reviewed-on: http://review.couchbase.org/40602
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>