Rebrand the comments in wallet_avoidreuse.py

Summary:
This one has a lot of comments affected, so put it into review alone.

Ref T1672.

Test Plan:

./test/functional/test_runner.py wallet_avoidreuse.py

Read the comments.

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Maniphest Tasks: T1672

Differential Revision: https://reviews.bitcoinabc.org/D9805