Update several rpc tests to work post fork.

Summary: Because of the replay protection, a lot of RPC tests do not function as expected post fork. This update several of them by putting the fork activation time far away in the past, essentially making the fork always on.

Test Plan: Run the tests

Reviewers: freetrader, CCulianu, #bitcoin_abc

Reviewed By: freetrader, CCulianu, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D430