[net processing] Remove CNode::nServices

Summary:
Use Peer::m_their_services instead

This is a partial backport of core#25514
https://github.com/bitcoin/bitcoin/pull/25514/commits/d9079fe18dc5d81ce290876353555b51125127d1

Depends on D14747

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14748