chore(core) rm Feature::RequestRule (#11866)

## Summary
This feature is now reasonably stable, let's remove it so we can
simplify our upcoming iterations here.

## Testing 
- [x] Existing tests pass

codex-rs/core/tests/suite/permissions_messages.rs

@@ -488,7 +488,6 @@ async fn permissions_message_includes_writable_roots() -> Result<()> {
         &sandbox_policy,
         AskForApproval::OnRequest,
         &Policy::empty(),
-        true,
         test.config.cwd.as_path(),
     )
     .into_text();