Bug 1388054 - Stop using Promise.jsm from devtools/shared/defer. r=jryans

MozReview-Commit-ID: DHEYqnPjMuG

--HG--
extra : rebase_source : 010303283d6d9f503de76e46b836e1f342f99353

devtools/shared/defer.js

@@ -4,11 +4,6 @@
 
 "use strict";
 
-// We have to keep using Promise.jsm here, because DOM Promises
-// start freezing during panel iframes destruction.
-// More info in bug 1454373 comment 15.
-const Promise = require("promise");
-
 /**
  * Returns a deferred object, with a resolve and reject property.
  * https://developer.mozilla.org/en-US/docs/Mozilla/JavaScript_code_modules/Promise.jsm/Deferred