Remove redundant interfaces

[hannakoppelaar]

This PR removes most interfaces that have only one implementation. Notable exceptions:

• Harvester, since this is meant as a crawler API
• Interfaces in the submit-to-rosetta module, in order to avoid merge conflicts with current development (they're only a handful we can do later)

[obrienben]

@leefrank9527 can you please review

[leefrank9527]

It simplified the WCT a lot and works well. Agree to merge this branch.