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 https://github.com/rust-lang/rust/pull/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`

compiler/rustc_passes/src/errors.rs

@@ -1670,13 +1670,6 @@ pub(crate) struct ProcMacroBadSig {
     pub kind: ProcMacroKind,
 }
 
-#[derive(Diagnostic)]
-#[diag(passes_skipping_const_checks)]
-pub(crate) struct SkippingConstChecks {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(LintDiagnostic)]
 #[diag(passes_unreachable_due_to_uninhabited)]
 pub(crate) struct UnreachableDueToUninhabited<'desc, 'tcx> {