service worker: Remove workaround for ServiceWorkerObjectHost crash.

Since issue 864731 was fixed in r576288, this workaround is no longer
needed.

Bug: 854993
Change-Id: I789dfb18cdb82ec51aa0ce5185586163c92269ec
Reviewed-on: https://chromium-review.googlesource.com/1147889Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577435}

content/browser/service_worker/service_worker_provider_host.cc

@@ -308,16 +308,6 @@ ServiceWorkerProviderHost::~ServiceWorkerProviderHost() {
   // TODO(falken): Use ScopedObserver instead of this explicit call.
   RemoveAllMatchingRegistrations();
 
-  // Explicitly destroy the ServiceWorkerObjectHosts and
-  // ServiceWorkerRegistrationObjectHosts owned by |this|. Otherwise, this
-  // destructor can trigger their Mojo connection error handlers, which would
-  // call back into halfway destroyed |this|. This is because they are
-  // associated with the ServiceWorker interface, which can be destroyed while
-  // in this destructor (|running_hosted_version_|'s |event_dispatcher_|). See
-  // https://crbug.com/854993.
-  service_worker_object_hosts_.clear();
-  registration_object_hosts_.clear();
-
   // This host may be destroyed before it received the anticipated
   // HintToUpdateServiceWorker IPC from the renderer. This can occur on
   // navigation failure or if the frame closed soon after navigation. The