Close issues on DOM repo

[LJWatson]

We need to close the issues on the W3C DOM repo and advise people to open new issues on the WHATWG DOM repo if the issue is still relevant.

Suggested message:

We're closing this issue on the W3C DOM specification because the W3C and WHATWG are now working together on HTML, and all issues are being discussed on the WHATWG repository.

If you filed this issue and you still think it is relevant, please open a new issue
on the WHATWG repository and reference this issue (if there is useful information here). Before you open a new issue, please check for existing issues on the WHATWG repository to avoid duplication.

If you have questions about this, please open an issue on the W3C HTML WG repository
or send an email to [email protected].