refactor(facade): remove dependency to rtts_assert

Closes #593

modules/angular2/src/facade/lang.es6

@@ -1,5 +1,3 @@
-export {proxy} from 'rtts_assert/rtts_assert';
-
 var _global = typeof window === 'undefined' ? global : window;
 export {_global as global};
 

modules/angular2/src/test_lib/test_lib.es6

@@ -1,5 +1,6 @@
 import {DOM} from 'angular2/src/facade/dom';
 
+export {proxy} from 'rtts_assert/rtts_assert';
 export var describe = window.describe;
 export var xdescribe = window.xdescribe;
 export var ddescribe = window.ddescribe;