Fixes #527 - $remove not correctly deleting Firebase data

Author: katowulf

src/FirebaseObject.js

@@ -85,7 +85,7 @@
           var self = this;
           $firebaseUtils.trimKeys(this, {});
           this.$value = null;
-          return self.$inst().$remove(self.$id).then(function(ref) {
+          return self.$inst().$remove().then(function(ref) {
             self.$$notify();
             return ref;
           });

tests/unit/FirebaseObject.spec.js

@@ -425,7 +425,7 @@ describe('$FirebaseObject', function() {
       expect(obj.$inst().$remove).not.toHaveBeenCalled();
       obj.$remove();
       flushAll();
-      expect(obj.$inst().$remove).toHaveBeenCalled();
+      expect(obj.$inst().$remove).toHaveBeenCalledWith(); // should not pass a key
     });
 
     it('should delete a primitive value', function() {