Permanently delete a role

Deletes the role identified by roleId under the tenant specified by the required tenant-id header. Use this to remove a role that is no longer needed; the role must exist at the time of the call. Returns 204 with no response body on success. Returns 400 if the tenant-id header is absent or blank. Note: if the role does not exist, the current implementation returns 500 rather than 404 (tracked in CP-36405); verify the ID via GET /roles.