ServiceWorker: remove get_newest_worker() helper (cleanup)

LayoutTests/http/tests/serviceworker/resources/test-helpers.js

 // Adapter for testharness.js-style tests with Service Workers
 
 function service_worker_unregister_and_register(test, url, scope) {
   if (!scope || scope.length == 0)
     return Promise.reject(new Error('tests must define a scope'));
 
   var options = { scope: scope };
   return service_worker_unregister(test, scope)
     .then(function() {
         return navigator.serviceWorker.register(url, options);
@@ skipping 48 matching lines @@
     });
   iframe.src = '';
   iframe.remove();
   return saw_unload;
 }
 
 function normalizeURL(url) {
   return new URL(url, document.location).toString().replace(/#.*$/, '');
 }
 
-function get_newest_worker(registration) {
-  if (!registration) {
-    return Promise.reject(new Error(
-      'get_newest_worker must be passed a ServiceWorkerRegistration'));
-  }
-  if (registration.installing)
-    return Promise.resolve(registration.installing);
-  if (registration.waiting)
-    return Promise.resolve(registration.waiting);
-  if (registration.active)
-    return Promise.resolve(registration.active);
-  return Promise.reject(new Error(
-    'registration must have at least one version'));
-}
-
 function wait_for_update(test, registration) {
   if (!registration || registration.unregister == undefined) {
     return Promise.reject(new Error(
       'wait_for_update must be passed a ServiceWorkerRegistration'));
   }
 
   return new Promise(test.step_func(function(resolve) {
       registration.addEventListener('updatefound', test.step_func(function() {
           resolve(registration.installing);
         }));
@@ skipping 163 matching lines @@
             channel.port1.onmessage = test.step_func(function() {
                 unload_iframe(frame).catch(function() {});
                 resolve();
               });
             frame.contentWindow.postMessage(
               {username: username, password: password, cookie: cookie},
               [channel.port2], origin);
           }));
     });
 }