assertQueries() was updated to wrap django-assert-queries, but this

ended up being invoked incorrectly, causing the assertion to always

succeed. We were yielding the result and not entering its context.
This change updates the call to simply return the assert_queries()'s

context manager directly. This avoids the issue and avoids wrapping in

another layer of context managers.
We also now depend on django-assert-queries 2.0.1, which, along with the

above, has the added benefit of not including assertQueries() in the

stack trace.

Djblets unit tests pass.