Remove legacy RecordStore support

[nazar-pc]

As you can see from usage locations, we've been using () implementation for quite some time, but farmer was still able to serve very old clients that relied on requests through Kademlia's DHT and its RecordStore implementation.

RecordStore has synchronous API and doesn't allow us to do more advanced iterative lookups, which is why we have implemented custom logic and abandoned RecordStore usage.

This moves DummyRecordStore from piece_provider module to constructor and simply prunes record store configuration option with all generics that it involved.

Code contributor checklist:

• I have read, understood and followed contributing guide

[teor2345]

Looks good!

I appreciate removing/replacing () with DummyRecordStore, I find code much more readable when I don’t have to guess what () means, and if it’s the same as the () in other parts of the code.