[test] Remove final references to mininode

Summary:
This concludes backport of core#19760 [4/4]
https://github.com/bitcoin/bitcoin/pull/19760/commits/d5800da5199527a366024bc80cad7fcca17d5c4a

There is a minor change to a comment that is missing in p2p_permissions.py because of a new test that is not yet backported.

Test Plan: ninja check-functional

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9575