Drop unused reverselock.h

Summary:
This is a partial backport of Core PR18234 : https://github.com/bitcoin/bitcoin/pull/18234/commits/cea19f685915be8affb2203184a549576194413f

Depends on D6533

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6535