unregistermethod of the
ServiceWorkerRegistrationinterface unregisters the service worker registration and returns a
Promise. The promise will resolve to
falseif no registration was found, otherwise it resolves to
trueirrespective of whether unregistration happened or not (it may not unregister if someone else just called
ServiceWorkerContainer.registerwith the same scope.) The service worker will finish any ongoing operations before it is unregistered.