Auto merge of #133321 - compiler-errors:const-checker, r=wesleywiser

Get rid of HIR const checker

As far as I can tell, the HIR const checker was implemented in rust-lang/rust#66170 because we were not able to issue useful const error messages in the MIR const checker.

This seems to have changed in the last 5 years, probably due to work like #90532. I've tweaked the diagnostics slightly and think the error messages have gotten *better* in fact.

Thus I think the HIR const checker has reached the end of its usefulness, and we can retire it.

cc `@RalfJung`