[ServiceWorker] Remove prefixMatch from CacheQueryOptions (#617)

Implementor feedback from both Chrome & Firefox suggests this will be a de-opt case.

I added it to the spec to implement the kind of prefix matching appcache had in FALLBACK rules, but I can't say I've used it in practice in demos and apps.

We can add it back later if we see devs recreating this & we think the browser can do it faster.

@wanderview is getting further Mozilla feedback, if he gives the go-ahead, let's remove it.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/617