Multiple references to missing PATENTS file

[Several files](https://github.com/search?q=repo%3Agraphql%2Fgraphiql%20PATENTS&type=code) in the project contain some version of the following license header:

> /**
> * Copyright (c) 2021 GraphQL Contributors
> * All rights reserved.
> *
> * This source code is licensed under the BSD-style license found in the
> * LICENSE file in the root directory of this source tree. An additional grant
> * of patent rights can be found in the PATENTS file in the same directory.
> */

However, no PATENTS file exists anywhere in the repository. Maybe a vestige of a former license? I suggest updating these headers to remove the reference to the PATENTS file.