[avalanche] Remove PeerManager::addNodeToPeer

Summary:
Replace it by a proof based API.

Depends on D6845 and D6848

Test Plan:

ninja all check-avalanche

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6850