Remove BIP9 CSV activation.

Summary: There is now an activation y height, so it's all good.

Test Plan:

make chck
./test/functional/test_runner.py --extended

Updated various tests

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1546