[avalanche] Expire queries once they reached their timeout.
So far, AvalancheProcessor leaks when a peer timesout. This ensures that queries that times out are effectively cleared with each event loop.
Depends on D2140
Test Plan: Added a test case.
Reviewers: #bitcoin_abc, Fabien
Reviewed By: Fabien
Subscribers: Fabien, teamcity, schancel
Differential Revision: https://reviews.bitcoinabc.org/D2143