Revert "feat(core): extract platforms out of core"

This reverts commit 3f4628c0b0.

modules/angular2/bootstrap.ts

@@ -1,5 +1,5 @@
 /**
- * See {@link bootstrap} for more information.
- * @deprecated
+ * This file is only used for dart applications and for internal examples
+ * that compile with both JavaScript and Dart.
  */
-export {bootstrap} from 'angular2/platform/browser';
+export {bootstrap} from 'angular2/src/core/bootstrap';