[avalanche] Fix wrong local proof status when a replacement one is received over p2p

Summary: There is an edge case where a replacement proof exists and is received over p2p, moving the local proof to the conflicting pool. If this proof was previously verified the status will be showing "pending verification" instead of "conflicting-utxos". This diff fixes this bug.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18347