Pass config down IsUAHFenabled instead of the chain params

Summary: We want to make the activation time configurable. The first step tward that goal is to make the config available where the check happens.

Test Plan:

make check

Reviewers: freetrader, sickpig, kyuupichan, awemany, #bitcoin_abc

Reviewed By: freetrader, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D217