ServiceWorker: Stop ServiceWorkerProviderContext from tracking SetVersionAttributes events

      This is a cleanup CL. ServiceWorkerProviderContext does not have to track
SetVersionAttributes events:

* For ServiceWorkerGlobalScope, SetVersionAttributes events are queued up in
ServiceWorkerProviderHost until the worker thread is started and then the events
are directly delivered to WebServiceWorkerRegistrationImpl.

* For (controlled) Document, the context does not care versions of the
associated registration.

BUG=532098

Review URL: https://codereview.chromium.org/1343113002

Cr-Commit-Position: refs/heads/master@{#349293}