Remove some of the UAHF activation logic.

Summary: It is not needed anymore and it will simplify the code.

Test Plan: Run the integration tests with the various fixes enabled ( D413, D411 and D409 ). Checks that they pass.

Reviewers: freetrader, CCulianu, #bitcoin_abc

Reviewed By: CCulianu, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D417