[avalanche] Remove the (node) PeerManager member from the avalanche processor

Summary:
This makes it possible to remove the net_processing.h header from the processor.
This is a step toward reducing the coupling between the avalanche and network layers.

Ref T1634.

Test Plan:

ninja all check-all
./contrib/teamcity/build-configurations.py lint-circular-dependencies

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Maniphest Tasks: T1634

Differential Revision: https://reviews.bitcoinabc.org/D9851