Remove service worker

[joeframbach]

Service worker attempts to load the service-worker runner from Google. The Thing has no internet access, so this will fail. There is no need for a service worker in this application. The user's device connects directly to the Thing, there is no need to precache static assets in the service worker. The user can just get it from the Thing directly.

[joeframbach]

The service worker file is generated by create-react-app but not used. Closing this ticket. An upgrade to create-react-app will remove the service worker file, since the behavior changed at some point.