[net processing] remove proof_relay parameter from Peer ctor

Summary:
This state is always the same for all the peers, and always defined during Init, as it only depends on whether the "-avalanche" command line option or config option was set.

Depends on D14740

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14741