[avalanche] Simplify the wait_for_proof test facility

Summary:
Let it take the expected status rather than flagging the orphan special case. This makes the tests more robust as we are sure of what is being tested.

Depends on D11802.

Test Plan:

ninja all check-extended

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Subscribers: sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D11809