Rollup merge of #112867 - compiler-errors:more-impl-source-nits, r=lcnr

More `ImplSource` nits

Even more clean-ups, I'll put this up in parallel with the `select_in_new_trait_solver` PR.

r? ``@lcnr``

compiler/rustc_ty_utils/src/instance.rs

@@ -293,9 +293,7 @@ fn resolve_associated_item<'tcx>(
                 None
             }
         }
-        traits::ImplSource::Param(..)
-        | traits::ImplSource::TraitAlias(..)
-        | traits::ImplSource::TraitUpcasting(_) => None,
+        traits::ImplSource::Param(..) | traits::ImplSource::TraitUpcasting(_) => None,
     })
 }