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

Author: IgorMinar

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 */
       },
 
       /**

test/ng/rootScopeSpec.js

@@ -898,6 +898,25 @@ describe('Scope', function() {
       var fn = child.$watch('somePath', function() {});
       expect(fn).toBe(noop);
     }));
+
+
+    it("should preserve all (own and inherited) model properties on a destroyed scope",
+        inject(function($rootScope) {
+      // This test simulates an async task (xhr response) interacting with the scope after the scope
+      // was destroyed. Since we can't abort the request, we should ensure that the task doesn't
+      // throw NPEs because the scope was cleaned up during destruction.
+
+      var parent = $rootScope.$new(),
+          child = parent.$new();
+
+      parent.parentModel = 'parent';
+      child.childModel = 'child';
+
+      child.$destroy();
+
+      expect(child.parentModel).toBe('parent');
+      expect(child.childModel).toBe('child');
+    }));
   });