[avalanche] Move testing the getavalanchepeerinfo RPC to its own test

Summary:
It's currently part of the voting test which is not where it belongs.

Ref T1634.

Test Plan:

./test/functional/test_runner.py abc_rpc_getavalanchepeerinfo

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Maniphest Tasks: T1634

Differential Revision: https://reviews.bitcoinabc.org/D9846