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

LayoutTests/http/tests/serviceworker/waiting.html

Index: LayoutTests/http/tests/serviceworker/waiting.html
diff --git a/LayoutTests/http/tests/serviceworker/waiting.html b/LayoutTests/http/tests/serviceworker/waiting.html
index e326f89763aadb6c2ae144e38b854cf15d6c8554..4ece274a3e5f2d9693a37a46a5b8097f20d1c6b5 100644
--- a/LayoutTests/http/tests/serviceworker/waiting.html
+++ b/LayoutTests/http/tests/serviceworker/waiting.html
@@ -21,10 +21,7 @@ async_test(function(t) {
       })
     .then(function(r) {
         registration = r;
-        return wait_for_update(t, registration);
-      })
-    .then(function(serviceWorker) {
-        return wait_for_state(t, serviceWorker, 'installed');
+        return wait_for_state(t, r.installing, 'installed');
       }, unreached_rejection(t, 'Registration should not fail'))
     .then(function() {
         var controller = frame.contentWindow.navigator.serviceWorker.controller;