[ServiceWorker] MessagePort[] no longer valid in WebIDL (#810)

the `T[]` array type has been removed from WebIDL, but Service Worker still uses it with `MessagePort[]` in `ServiceWorkerMessageEvent` and `ExtendableMessageEvent`.

Also, it applies the `[SameObject]` extended attribute to those, but `[SameObject]` is not supposed to be applied to arrays, only to interface types.

---
Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/810