feat(asDirective): match $destroy behaviour with ctrl.$onDestroy (see angular#14127)

Author: drpicox

src/ng/directive/as.js

@@ -66,7 +66,7 @@ var componentAsDirective = ['$parse', function($parse) {
         setter(scope, controller);
 
         // when the element is removed, remove it from the scope assignment (nullify it)
-        iElement.on('$destroy', function() {
+        scope.$on('$destroy', function() {
           setter(scope, null);
         });
       };