[net] remove CConnman::AddNewAddresses

Summary:

It just forwards calls to CAddrMan::Add.

Partial backport of core#20228:
https://github.com/bitcoin/bitcoin/pull/20228/commits/7c4cc67c0c3c50df004ee53cac5b2884b7fbab29

Depends on D12249.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12250