Rollup merge of #140317 - mejrs:check_on_uni, r=compiler-errors

Remove redundant check

We still check for `rustc_on_unimplemented` on implementations, but this functionality was removed in https://github.com/rust-lang/rust/pull/139091, since then it always returns `Ok` when called with a non-trait defid.

b4c8b0c3f0/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs (L557-L564)

compiler/rustc_hir_analysis/src/check/check.rs

@@ -730,7 +730,6 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) {
                     .is_ok()
                 {
                     check_impl_items_against_trait(tcx, def_id, impl_trait_header);
-                    check_on_unimplemented(tcx, def_id);
                 }
             }
         }