Remove service worker from v4.0 and v4.1.

docs/4.0/assets/js/src/pwa.js

@@ -1,17 +0,0 @@
-/* eslint no-console:off */
-
-(function () {
-  'use strict'
-
-  if ('serviceWorker' in navigator) {
-    window.addEventListener('load', function () {
-      navigator.serviceWorker.register('/sw.js').then(function (registration) { // eslint-disable-line compat/compat
-        console.log('ServiceWorker registration successful with scope: ', registration.scope)
-      }).catch(function (err) {
-        console.log('ServiceWorker registration failed: ', err)
-      })
-    })
-  } else {
-    console.log('Service workers are not supported.')
-  }
-}())