dillon1000/react

Forbid full-page rendering without server rendering

Final part of server rendering cleanup. We should only support full-page rendering when server rendering is involved since
otherwise it's slow and can crash browsers when you start adding and removing document roots. This diff removes the magic
innerHTML code (since that will be handled by the server rendering piece) and adds the right assertions and errors.

Because there's no longer a dangerous of accidentally nuking the whole page, I removed allowFullPageRender which is yet another
internal we no longer need to expose.