Remove all fixed function pipeline code within Recoil.

Fixed function pipelines are ancient at this point and are far from a priority on any driver. I propose removing them from recoil completely.

Part of my motivation is preparing recoil to switch to a backend-agnostic renderer in the future though that is quite far off.

I'd be willing to take this on myself (with a lot of claude usage) if someone gives me the green light.

The issue names no files, tests, or entry points. Start by locating all fixed-function pipeline code in the Recoil source and mapping its dependencies, then determine the complete removal boundary and how the project verifies that no such code remains.

Written by the indexing model from the issue text.