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/benchpress/test/metric/multi_metric_spec.ts

@@ -12,7 +12,7 @@ import {
 } from 'angular2/testing_internal';
 
 import {ListWrapper} from 'angular2/src/facade/collection';
-import {PromiseWrapper, Promise} from 'angular2/src/facade/async';
+import {PromiseWrapper} from 'angular2/src/facade/async';
 
 import {Metric, MultiMetric, bind, provide, Injector} from 'benchpress/common';
 

modules/benchpress/test/metric/perflog_metric_spec.ts

@@ -12,7 +12,7 @@ import {
 } from 'angular2/testing_internal';
 
 import {StringMapWrapper} from 'angular2/src/facade/collection';
-import {PromiseWrapper, Promise} from 'angular2/src/facade/async';
+import {PromiseWrapper} from 'angular2/src/facade/async';
 import {isPresent, isBlank} from 'angular2/src/facade/lang';
 
 import {

modules/benchpress/test/reporter/multi_reporter_spec.ts

@@ -11,7 +11,7 @@ import {
   xit,
 } from 'angular2/testing_internal';
 
-import {PromiseWrapper, Promise} from 'angular2/src/facade/async';
+import {PromiseWrapper} from 'angular2/src/facade/async';
 import {DateWrapper} from 'angular2/src/facade/lang';
 
 import {Reporter, MultiReporter, bind, provide, Injector, MeasureValues} from 'benchpress/common';

modules/benchpress/test/runner_spec.ts

@@ -24,7 +24,7 @@ import {
   SampleState
 } from 'benchpress/common';
 import {isBlank} from 'angular2/src/facade/lang';
-import {Promise, PromiseWrapper} from 'angular2/src/facade/async';
+import {PromiseWrapper} from 'angular2/src/facade/async';
 
 export function main() {
   describe('runner', () => {

modules/benchpress/test/sampler_spec.ts

@@ -12,7 +12,7 @@ import {
 } from 'angular2/testing_internal';
 
 import {isBlank, isPresent, stringify, Date, DateWrapper} from 'angular2/src/facade/lang';
-import {PromiseWrapper, Promise} from 'angular2/src/facade/async';
+import {PromiseWrapper} from 'angular2/src/facade/async';
 
 import {
   Sampler,