Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Remove request context mapper
http.Request now allows setting/retrieving a per-request context, which removes the need for plumbing a request-context mapper throughout the stack
In addition to being way simpler, this has the benefit of removing a potentially contentious lock object from the handling path
This PR:
* removes RequestContextMapper
* converts context fetchers to use `req.Context()`
* converts context setters to use `req = req.WithContext(...)`
* updates filter plumbing in two places (audit and timeout) to properly return the request with modified context
* updates tests that used a fake context mapper to set the context in the request instead
Fixes https://github.com/kubernetes/kubernetes/issues/62796
```release-note
NONE
```
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