Don't merge: upgrade simple-dom

[chancancode]

The actual implementation of simple-dom (now fully typed) is not compatible with Simple.*. Specifically, it does not support namespaces. Removing them from Simple.* yields around type 20 errors:

Most of these are in tests. However, I do think there is a real issue. Specifically, in SSR mode, we are wrongly assuming we can call NS methods like createElementNS. I don't know if this causes problems in practice – maybe a combination of things causes these things to never be called in practice, but we should get the types to more accurately reflect reality.

Also, since simple-dom is now fully typed, and is a strict subset of DOM, do we still need Simple.*?

[tomdale]

I think this is superseded by #866.