Service Worker: Clients.matchAll() IDL nit

Source/modules/serviceworkers/Clients.idl

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#clients-interface
 [
     Exposed=ServiceWorker,
     RuntimeEnabled=ServiceWorker,
     GarbageCollected,
     TypeChecking=Interface,
     ImplementedAs=ServiceWorkerClients,
 ] interface Clients {
-    [CallWith=ScriptState] Promise<sequence<Client>?> matchAll(optional ClientQueryOptions options);
+    [CallWith=ScriptState] Promise<sequence<Client>> matchAll(optional ClientQueryOptions options);
     [RuntimeEnabled=ServiceWorkerClientAttributes, CallWith=ScriptState] Promise<WindowClient?> openWindow(USVString url);
     [CallWith=ScriptState] Promise<void> claim();
 };