Per the deprecation warnings (which have been raised since DRF 3.11),
`set_context()` was planned not to be supported in DRF 3.13. I think we
can safely delete it, in favor of `requires_context`.
From the 3.11 announcement:
> Previous our approach to this was that implementations could include a
> `set_context` method, which would be called prior to validation. However
> this approach had issues with potential race conditions. We have now
> move this approach into a pending deprecation state. It will continue to
> function, but will be escalated to a deprecated state in 3.12, and
> removed entirely in 3.13.
Why keep `RemovedInDRF313Warning` around?
=========================================
It's a bit odd that version 3.13 includes an exception class describing
things which are to be deleted in 3.13, but I've opted to keep the (now
unreferenced) class around, for fear of breaking others' setup.
(For example, if projects have a `filterwarnings` setup meant to
intercept `rest_framework.RemovedInDRF313Warning`, an error will be
thrown due to an unresolvable reference).
8b2ccccbe5