T2684

Part 1 of a stacked diff to patch issue where Cashtab's 'cache first' service worker will not deliver the latest version of Cashtab without a hard refresh.

In this part, the existing service worker is removed.

npm start
Open the dev console. Go to the Application tab and click "Service Workers." Observe no service workers in the pane.
Do the same at Cashtab.com. Observe there is a service worker.