Checkbox/Radio: Investigate removing no-input-element fallback logic

[kfranqueiro]

We currently have this code in radio, and similar code in checkbox:

https://github.com/material-components/material-components-web/blob/v0.35.0/packages/mdc-radio/foundation.js#L84-L94

This includes code that falls back to a dummy object if a native input isn't found.

I'm fairly certain this was done to appease closure compiler, but I don't think we should even need this fallback in order to do that. (FWIW, this fallback has existed in code since 1.5 years ago.)

The reason it's perhaps a bit problematic is because it leaks complexity into our API docs (and probably also tests, if I had to guess).