[5 of 5] Style cleanup.

Summary:
last partial PR15118 backport
https://github.com/bitcoin/bitcoin/pull/15118/commits/04cca330944f859b4ed68cb8da8a79f5206fd630

Depends on D3588

Test Plan: make check

Reviewers: deadalnix, Fabien, jasonbcox, #bitcoin_abc

Reviewed By: deadalnix, jasonbcox, #bitcoin_abc

Maniphest Tasks: T631

Differential Revision: https://reviews.bitcoinabc.org/D3589