[avalanche] Expire queries once they reached their timeout.

Summary:
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