Test OP_RETURN anti replay feature

Summary: As per title. This extends the test for activation to ensure OP_RETURN antireplay also triggers properly.

Test Plan:

../qa/pull-tester/rpc-tests.py abc-p2p-activation.py

Reviewers: freetrader, sickpig, awemany, kyuupichan, #bitcoin_abc

Reviewed By: freetrader, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D197