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 This also cleans up a little bit of adjacent code that was very out of date. Testing Done: Ran unit tests.