opportunistic 1p1c followups

Summary:
Backport of core#30012.

The first 2 commits are irrelevant to us.

Depends on D16494.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16498