Remove incorrect tests for AggregateError#toString (#2435)

A conforming implementation of ECMAScript may provide additional types, values, objects, properties, and functions beyond those described in this specification. In particular, a conforming implementation of ECMAScript may provide properties not described in this specification, and values for those properties, for objects that are described in this specification.

Ref #2433

test/built-ins/AggregateError/toString.js

@@ -1,29 +0,0 @@
-// Copyright (C) 2019 Leo Balter. All rights reserved.
-// This code is governed by the BSD license found in the LICENSE file.
-
-/*---
-description: >
-  Instance reuses the toString from Error.prototype
-esid: sec-aggregate-error
-info: |
-  Ref https://github.com/tc39/proposal-promise-any/pull/49
-
-  Properties of the AggregateError Constructor
-
-  - has a [[Prototype]] internal slot whose value is the intrinsic object %Error%.
-features: [AggregateError]
----*/
-
-assert.sameValue(
-  AggregateError.prototype.toString,
-  Error.prototype.toString,
-  'AggregateError inherits the toString method from Error.prototype'
-);
-
-var sample = new AggregateError([], '');
-
-assert.sameValue(
-  sample.toString,
-  Error.prototype.toString,
-  'toString is inherited from Error.prototype'
-);