SSH is deployed inside Kubernetes cluster where rate limiting
at the application layer is unnecessary. Remove all SSH rate
limiter code:
- SshRateLimiter from SSHandle and SSHServer structs
- is_user_allowed checks in auth_publickey, auth_publickey_offered
- is_repo_access_allowed in exec_request
- is_ip_allowed in server::new_client
- rate_limiter module and start_cleanup