set referrer in window.load_url

- this conforms to follow-hyperlinks spec step 13
- this conforms to window-open spec step 14.3
- replace uses of `referrer_url` with `referrer`
- in Request class, change "no-referrer" to ""
- set websocket fetch referrer to "no-referrer"

components/script/dom/workerglobalscope.rs

@@ -213,9 +213,8 @@ impl WorkerGlobalScopeMethods for WorkerGlobalScope {
                 .use_url_credentials(true)
                 .origin(global_scope.origin().immutable().clone())
                 .pipeline_id(Some(self.upcast::<GlobalScope>().pipeline_id()))
-                .referrer_url(None)
                 .referrer_policy(None);
-;
+
             let (url, source) =
                 match load_whole_resource(request, &global_scope.resource_threads().sender()) {
                     Err(_) => return Err(Error::Network),