[avalanche] Rename proof filter to match rest of the code base

Summary:
rejectedProofs is confusing because these proofs are strictly only invalid due to consensus or invalidated by avalanche.
The avalanche module uses "invalidated" to mean proofs that were finalized in the rejected state. This patch makes the naming consistent.

Test Plan:

ninja check check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11963