Auto merge of rust-lang#103284 - compiler-errors:const-sad, r=oli-obk

Revert "Unify tcx.constness and param env constness checks"

Too much of a perf regression rust-lang#102975 (comment), and an attempt in rust-lang#103263 didn't fix it except for just a tiny bit.

This change isn't really needed (see rust-lang#102830 (comment)), so this should be an easy revert.