Remove monolith activation altogether

Summary: Monolith was purely additive. Now that it is activated, we can consider it as it if always was activated.

Test Plan:

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

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1483