Fix all pyflakes warnings in Djblets.
Review Request #11621 — Created May 26, 2021 and submitted
Djblets 2.x had a large number of pyflakes warnings, largely as a result
of removed deprecated code. Most of this was harmless, but a few unit
tests were obscured due to reused function names.
This change cleans up all the warnings found for Djblets 2.x.
Unit tests pass.
Pyflakes showed 0 warnings.