clean up some tests that needlessly use -replayprotectionactivationtime

Summary: (I suppose it was there for activation purposes then didn't get cleaned up)

Test Plan:

test_runner.py abc-magnetic-anomaly-mining.py
test_runner.py abc-p2p-fullblocktest.py
test_runner.py abc-transaction-ordering.py

Reviewers: Fabien, #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4746