[Linter] Fix all the lint warnings

Summary: A few lint warnings sneaked into the codebase, fix them all.

Test Plan:

arc lint --everything

Should return no error.

Depends on D12726 for the test plan.

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D12728