Early on in Django history, the built-in `Manager.get_or_create` method was racy, potentially raising `IntegrityError`. We had built a `ConcurrencyManager` to handle this case, and used it for many of our models where we encountered issues. As of quite some time ago, Django's built-in `Manager` does exactly the same thing as our `ConcurrencyManager` did, and we just didn't discover that because everything was working as expected. We've deprecated the ConcurrencyManager as a result. This change swaps out all our usage to just use the built-in `Manager` class. Testing Done: Ran unit tests.