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/exec_policy.rs

@@ -686,8 +686,6 @@ mod tests {
     use crate::config_loader::ConfigLayerStack;
     use crate::config_loader::ConfigRequirements;
     use crate::config_loader::ConfigRequirementsToml;
-    use crate::features::Feature;
-    use crate::features::Features;
     use codex_app_server_protocol::ConfigLayerSource;
     use codex_protocol::protocol::AskForApproval;
     use codex_protocol::protocol::SandboxPolicy;
@@ -1281,8 +1279,6 @@ prefix_rule(
             "cargo-insta".to_string(),
         ];
         let manager = ExecPolicyManager::default();
-        let mut features = Features::with_defaults();
-        features.enable(Feature::RequestRule);
 
         let requirement = manager
             .create_exec_approval_requirement_for_command(ExecApprovalRequest {