Removed obsolete dependencies

[tHBp]

The service worker cache polyfill used is now declared obsolete according to repository maintainer(s) as support for cache.addAll is now available in Chrome Stable as well as Opera Stable. See this.

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[tHBp]

I've signed it.

[googlebot]

CLAs look good, thanks!

[tHBp]

Any update on this?

[Ganyanut]

I signed it!

[tHBp]

Any updates? Pardon me if I'm being hasty, as I'm not familiar with the approval/access flow for merging pull requests to repositories maintained by Google.

[jeffposnick]

Sorry about that—thanks for the contribution. Agreed that the polyfill shouldn't be necessary anymore.