Enable use_once_callback on mojom GN rule by default

services/identity/public/interfaces/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
   sources = [
     "identity_manager.mojom",
   ]
 
   public_deps = [
     ":constants",
     "//components/signin/public/interfaces",
   ]
+
+  # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
+  use_once_callback = false
 }
 
 mojom("constants") {
   sources = [
     "constants.mojom",
   ]
 }