[fullscreen] Issues with the removing steps (#29)

In the current spec, the substep 2.1 is:
> If node is its node document's fullscreen element, exit fullscreen that document **and terminate these steps.**

The bold part should be removed, because we have removed the hierarchy restriction, and thus we may continue reaching other elements in the top layer after exiting fullscreen from the current fullscreen element.

In addition, I believe this removing steps should cover the whole top layer, instead of only fullscreen elements.

(BTW, I wonder what would happen if I request fullscreen on a model `<dialog>` or make a fullscreened `<dialog>` modal...)

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fullscreen/issues/29