[avalanche] Fix some naming nits

Summary:
They slipped through the last few commits. There is no change in behavior.

Ref T1854.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Maniphest Tasks: T1854

Differential Revision: https://reviews.bitcoinabc.org/D10248