[ServiceWorker] Remove client request requirement from respondWith() (#725)

> If response.type is "opaque", and request's associated request is a client request, set the respond-with error flag.

This is already a requirement per Fetch and done somewhat better there. `respondWith()` should just passthrough any response.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/725