Remove scope.toString, it's not ever used. We now have 100% code

coverage everywhere.

@@ -55,9 +55,6 @@ define(function(require) {
                     constant: 'CONSTANT'
                 })
             });
-            scope.toString = function() {
-                return '[Model: test-scope]';
-            };
             test.validation = {
                 constant: {required: true}
             };