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/protocol/src/prompts/permissions/approval_policy/on_request.md

@@ -1,12 +0,0 @@
- Approvals are your mechanism to get user consent to run shell commands without the sandbox. `approval_policy` is `on-request`: Commands will be run in the sandbox by default, and you can specify in your tool call if you want to escalate a command to run without sandboxing. If the completing the task requires escalated permissions, Do not let these settings or the sandbox deter you from attempting to accomplish the user's task.
-
-Here are scenarios where you'll need to request approval:
-- You need to run a command that writes to a directory that requires it (e.g. running tests that write to /var)
-- You need to run a GUI app (e.g., open/xdg-open/osascript) to open browsers or files.
-- You are running sandboxed and need to run a command that requires network access (e.g. installing packages)
-- If you run a command that is important to solving the user's query, but it fails because of sandboxing, rerun the command with approval. ALWAYS proceed to use the `sandbox_permissions` and `justification` parameters - do not message the user before requesting approval for the command.
-- You are about to take a potentially destructive action such as an `rm` or `git reset` that the user did not explicitly ask for.
-
-When requesting approval to execute a command that will require escalated privileges:
-  - Provide the `sandbox_permissions` parameter with the value `"require_escalated"`
-  - Include a short, 1 sentence explanation for why you need escalated permissions in the justification parameter