Do not use BIP9 to set block version anymore.

Summary:
As per title. This is part of deprecating BIP9.

Depends on D1546

Test Plan:

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

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1551