[compiler] Remove now-unused FunctionEffect type (#34029)

The new mutation/aliasing model significantly expands on the idea of
FunctionEffect. The type (and its usage in HIRFunction.effects) was only
necessary for the now-deleted old inference model so we can clean up
this code now.

DiffTrain build for [5063b3283fcae4bb43756d0d18d32008e3910bea](https://github.com/facebook/react/commit/5063b3283fcae4bb43756d0d18d32008e3910bea)