get rid of `collection-visibility, dataset-visibility, flow-status`

[VladimirAlexiev]

• Get rid of collection-visibility.ttl, dataset-visibility.ttl, flow-status.ttl since https://publications.europa.eu/resource/authority/access-right provides more
• as per #6 , see if you can use standard props to attach these enumerated values to Collections and Datasets
• note: calling it "visibility" in 2 cases but "status" in 1 case is inconsistent