DOMException is no longer a part of the grammar

[domenic]

I'm not sure what impact this would actually have in terms of output, but, whatwg/webidl@5c8eb31 + whatwg/webidl@b085536 moved DOMException from being a built-in type (like object) to being one defined via an interface declaration (like HTMLHtmlElement). So, parsers should no longer need to have any code related to it. I found a bit of code related to it in this repo, so I thought I'd file an issue so you could track removing it.