fix(compiler): remove AppRootUrl

Related to #5815

This should not break anything because AppRootUrl wasn't actually
being used by the compiler anymore.

modules/angular2/web_worker/worker.ts

@@ -1,6 +1,6 @@
 export * from '../common';
 export * from '../core';
 export * from '../platform/worker_app';
-export {UrlResolver, AppRootUrl} from '../compiler';
+export {UrlResolver} from '../compiler';
 export * from '../instrumentation';
 export * from 'angular2/src/platform/worker_app';