chore(lint): remove unused imports (#11923)

This was done automatically by tslint, which can now fix issues it finds.
The fixer is still pending in PR https://github.com/palantir/tslint/pull/1568
Also I have a local bugfix for https://github.com/palantir/tslint/issues/1569
which causes too many imports to be deleted.

modules/@angular/platform-browser-dynamic/src/private_export.ts

@@ -5,7 +5,7 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import {ClassProvider, ExistingProvider, FactoryProvider, Provider, TypeProvider, ValueProvider} from '@angular/core';
+
 import {INTERNAL_BROWSER_DYNAMIC_PLATFORM_PROVIDERS} from './platform_providers';
 import * as resource_loader from './resource_loader/resource_loader_impl';