Remove ::fRequireStandard global

Summary:
This is a partial backport of core#25648
https://github.com/bitcoin/bitcoin/pull/25648/commits/fa148602e67fe035b1b21eff6c0b656919ac2d45

Depends on D15751

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15752