The underlying Djblets TestCase.assertQueries() has had a deprecation

warning, but Review Board didn't. This still triggered warnings, but the

line number associated with those made it harder to find the actual

instances, since it'd just show the call to super().assertQueries().

This change marks the subclass version for deprecation at the matching

version to when we'll be removing the Djblets one.
This also cleans up a little bit of adjacent code that was very out of

date.

Ran unit tests.