fix(Scope): revert the __proto__ cleanup as that could cause regressions

When a async task interacts with a scope that has been destroyed already
and if it interacts with a property that is prototypically inherited from
some parent scope then resetting proto would make these inherited properties
inaccessible and would result in NPEs

src/ng/rootScope.js

@@ -757,14 +757,6 @@ function $RootScopeProvider(){
         // prevent NPEs since these methods have references to properties we nulled out
         this.$destroy = this.$digest = this.$apply = noop;
         this.$on = this.$watch = function() { return noop; };
-
-
-        /* jshint -W103 */
-        // not all browsers have __proto__ so check first
-        if (this.__proto__) {
-          this.__proto__ = null;
-        }
-        /* jshint +W103 */
       },
 
       /**