Remove Session.trait_methods_not_found

Instead, avoid registering the problematic well-formed obligation
to begin with. This removes global untracked mutable state,
and avoids potential issues with incremental compilation.

compiler/rustc_infer/src/traits/error_reporting/mod.rs

@@ -104,11 +104,5 @@ pub fn report_object_safety_error(
          to be resolvable dynamically; for more information visit \
          <https://doc.rust-lang.org/reference/items/traits.html#object-safety>",
     );
-
-    if tcx.sess.trait_methods_not_found.borrow().iter().any(|full_span| full_span.contains(span)) {
-        // Avoid emitting error caused by non-existing method (#58734)
-        err.cancel();
-    }
-
     err
 }