Inheritance was overkill here, and now we can use inheritance for new functionality X
without having to create classes for all combinations of {X, is_testnet}.
- unused
- the client was already refusing to fund such lockup addresses (if the server asked)
- no existing unit tests for it, and as the choice is up to the server, it is hard to create tests
- no clear reason to want to use p2sh-nested scripts here, aside from curiosity