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.

Ran unit tests.