docs(change_detection): don't annotate exports that are already in public modules

Since `DynamicChangeDetection` and `JitChangeDetection` classes are alreadt in the
public module, they do not need to be annotated with a `@exportAs` tag

Closes angular#1353

Author: petebacondarwin

modules/angular2/change_detection.js

@@ -51,9 +51,6 @@ export var defaultPipes = {
 };
 
 
-/**
- * @exportedAs angular2/change_detection
- */
 export class DynamicChangeDetection extends ChangeDetection {
   registry:PipeRegistry;
 
@@ -67,9 +64,6 @@ export class DynamicChangeDetection extends ChangeDetection {
   }
 }
 
-/**
- * @exportedAs angular2/change_detection
- */
 export class JitChangeDetection extends ChangeDetection {
   registry:PipeRegistry;