[clipboard-apis] Move script-created events out of "fire a clipboard event" (#16)

Scripts have no entry path into the "fire a clipboard event" algorithm, so this algorithm can assume that the source of the event is the user agent.

"Let trusted be true if the event is generated by the user agent, false otherwise" and "Else, if the event is generated by a script" can both be removed and much simplified.

For script-fired events, there shouldn't be anything at all to say, because it's the code dispatching the event which performs the default action. (See https://github.com/w3c/clipboard-apis/issues/14)

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/clipboard-apis/issues/16