Remove requestIdleCallback/cancelIdleCallback flow lib

Summary: As of flow 0.36.0, `requestIdleCallback` and `cancelIdleCallback` are part of the builtin lib defs. https://github.com/facebook/flow/pull/2800

Reviewed By: yungsters

Differential Revision: D4280306

fbshipit-source-id: 30328675c7dbfe12f603321f1196c87800a19ba8

flow/global.js

@@ -1,17 +0,0 @@
-/**
- * Copyright (c) 2015-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- *
- * @flow
- * @nolint
- */
-
-/* eslint-disable */
-
-// Add missing flow definitions, can be removed when included in flow.
-declare function requestIdleCallback(callback: any): number;
-declare function cancelIdleCallback(idleCallbackId: ?number): void;