[clipboard-apis] Definition of editing host (#20)

Under 5. Terminology there is a link to a link to an API (under 4. APIs from other specs) to [editing host](https://w3c.github.io/editing/#editing-host). The partial of that link however, doesn't exist, leading readers to keep and wonder what an editing host is ;)

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/clipboard-apis/issues/20