Rollup merge of #135378 - compiler-errors:unnecessary-stashing, r=chenyukang

Remove a bunch of diagnostic stashing that doesn't do anything

#121669 removed a bunch of conditional diagnostic stashing/canceling, but left around the `steal` calls which just emitted the error eagerly instead of canceling the diagnostic. I think that these no-op `steal` calls don't do much and are confusing to encounter, so let's remove them.

The net effect is:
1. We emit more duplicated errors, since stashing has the side effect of duplicating diagnostics. This is not a big deal, since outside of `-Zdeduplicate-diagnostics=no`, the errors are already being deduplicated by the compiler.
2. It changes the order of diagnostics, since we're no longer stashing and then later stealing the errors. I don't think this matters much for the changes that the UI test suite manifests, and it makes these errors less order dependent.

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -152,7 +152,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                         let (Ok(e) | Err(e)) = prev
                             .build_mismatch_error(
                                 &OpaqueHiddenType { ty, span: concrete_type.span },
-                                opaque_type_key.def_id,
                                 infcx.tcx,
                             )
                             .map(|d| d.emit());