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/src/codex.rs

@@ -2004,7 +2004,6 @@ impl Session {
                 &next.sandbox_policy,
                 next.approval_policy,
                 self.services.exec_policy.current().as_ref(),
-                self.features.enabled(Feature::RequestRule),
                 &next.cwd,
             )
             .into(),
@@ -2624,7 +2623,6 @@ impl Session {
                 &turn_context.sandbox_policy,
                 turn_context.approval_policy,
                 self.services.exec_policy.current().as_ref(),
-                self.features.enabled(Feature::RequestRule),
                 &turn_context.cwd,
             )
             .into(),