[refactor] Remove IsOutboundDisconnectionCandidate

Summary:
Partial backport (18/19) of core PR19316:
https://github.com/bitcoin/bitcoin/pull/19316/commits/bc5d65b3ca41eebb1738fdda4451d1466e77772e

Depends on D8727.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8728