fix(typing): Remove re-export of the Promise built-in type.

Instead, ts2dart can add the 'dart:async' import whenever
Promise is used.

Fixes #6468

modules/angular2_material/src/components/dialog/dialog.ts

@@ -16,7 +16,7 @@ import {
   ViewEncapsulation
 } from 'angular2/core';
 
-import {ObservableWrapper, Promise, PromiseWrapper} from 'angular2/src/facade/async';
+import {ObservableWrapper, PromiseWrapper} from 'angular2/src/facade/async';
 import {isPresent, Type} from 'angular2/src/facade/lang';
 import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {MouseEvent, KeyboardEvent} from 'angular2/src/facade/browser';