ServiceWorker cleanup: remove wait_for_update() in favor of r.installing in most tests

LayoutTests/http/tests/serviceworker/active.html

Index: LayoutTests/http/tests/serviceworker/active.html
diff --git a/LayoutTests/http/tests/serviceworker/active.html b/LayoutTests/http/tests/serviceworker/active.html
index e2d5bb037267d90583586b2578b773635c258e36..90bae187a4ba494bf2cf0b367f0755b2606d5e36 100644
--- a/LayoutTests/http/tests/serviceworker/active.html
+++ b/LayoutTests/http/tests/serviceworker/active.html
@@ -21,10 +21,7 @@ async_test(function(t) {
         }))
       .then(step(function(r) {
           registration = r;
-          return wait_for_update(t, registration);
-        }))
-      .then(step(function(serviceWorker) {
-          return wait_for_state(t, serviceWorker, 'activating');
+          return wait_for_state(t, r.installing, 'activating');
         }))
       .then(step(function() {
           var container = frame.contentWindow.navigator.serviceWorker;