Revert of Disable non-standard Promise functions in staging

src/js/promise-extra.js

Index: src/js/promise-extra.js
diff --git a/src/js/promise-extra.js b/src/js/promise-extra.js
deleted file mode 100644
index 2613a500ded843aeb54d134846c0c1618d177beb..0000000000000000000000000000000000000000
--- a/src/js/promise-extra.js
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright 2015 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-(function(global, utils) {
-
-"use strict";
-
-%CheckIsBootstrapping();
-
-var GlobalPromise = global.Promise;
-
-var PromiseChain = utils.ImportNow("PromiseChain");
-var PromiseDeferred = utils.ImportNow("PromiseDeferred");
-var PromiseResolved = utils.ImportNow("PromiseResolved");
-
-utils.InstallFunctions(GlobalPromise.prototype, DONT_ENUM, [
-  "chain", PromiseChain,
-]);
-
-%InstallToContext([
-  "promise_chain", PromiseChain,
-]);
-
-utils.InstallFunctions(GlobalPromise, DONT_ENUM, [
-  "defer", PromiseDeferred,
-  "accept", PromiseResolved,
-]);
-
-})