msglist test [nfc]: Unify setup functions

Each of the test cases calls setupStore and then uses the resulting
store for just one thing, namely passing it to messageListViewWithMessages.
So just subsume the former into the latter.

test/model/message_list_test.dart

@@ -5,7 +5,6 @@ import 'package:zulip/api/model/model.dart';
 import 'package:zulip/api/route/messages.dart';
 import 'package:zulip/model/message_list.dart';
 import 'package:zulip/model/narrow.dart';
-import 'package:zulip/model/store.dart';
 
 import '../api/fake_api.dart';
 import '../api/model/model_checks.dart';
@@ -15,7 +14,7 @@ import '../model/test_store.dart';
 
 const int userId = 1;
 
-Future<PerAccountStore> setupStore(ZulipStream stream) async {
+Future<MessageListView> messageListViewWithMessages(List<Message> messages, ZulipStream stream, Narrow narrow) async {
   addTearDown(TestZulipBinding.instance.reset);
 
   await TestZulipBinding.instance.globalStore.add(eg.selfAccount, eg.initialSnapshot());
@@ -24,10 +23,6 @@ Future<PerAccountStore> setupStore(ZulipStream stream) async {
   store.addUser(eg.user(userId: userId));
   store.addStream(stream);
 
-  return store;
-}
-
-Future<MessageListView> messageListViewWithMessages(List<Message> messages, PerAccountStore store, Narrow narrow) async {
   final messageList = MessageListView.init(store: store, narrow: narrow);
 
   final connection = store.connection as FakeApiConnection;
@@ -51,11 +46,10 @@ void main() async {
   final narrow = StreamNarrow(stream.streamId);
 
   test('findMessageWithId', () async {
-    final store = await setupStore(stream);
     final m1 = eg.streamMessage(id: 2, stream: stream);
     final m2 = eg.streamMessage(id: 4, stream: stream);
     final m3 = eg.streamMessage(id: 6, stream: stream);
-    final messageList = await messageListViewWithMessages([m1, m2, m3], store, narrow);
+    final messageList = await messageListViewWithMessages([m1, m2, m3], stream, narrow);
 
     // Exercise the binary search before, at, and after each element of the list.
     check(messageList.findMessageWithId(1)).equals(-1);
@@ -69,13 +63,11 @@ void main() async {
 
   group('maybeUpdateMessage', () {
     test('update a message', () async {
-      final store = await setupStore(stream);
-
       final originalMessage = eg.streamMessage(id: 243, stream: stream,
         content: "<p>Hello, world</p>",
         flags: [],
       );
-      final messageList = await messageListViewWithMessages([originalMessage], store, narrow);
+      final messageList = await messageListViewWithMessages([originalMessage], stream, narrow);
 
       final updateEvent = UpdateMessageEvent(
         id: 1,
@@ -110,11 +102,9 @@ void main() async {
     });
 
     test('ignore when message not present', () async {
-      final store = await setupStore(stream);
-
       final originalMessage = eg.streamMessage(id: 243, stream: stream,
         content: "<p>Hello, world</p>");
-      final messageList = await messageListViewWithMessages([originalMessage], store, narrow);
+      final messageList = await messageListViewWithMessages([originalMessage], stream, narrow);
 
       final updateEvent = UpdateMessageEvent(
         id: 1,
@@ -139,12 +129,10 @@ void main() async {
 
     // TODO(server-5): Cut legacy case for rendering-only message update
     Future<void> checkRenderingOnly({required bool legacy}) async {
-      final store = await setupStore(stream);
-
       final originalMessage = eg.streamMessage(id: 972, stream: stream,
         lastEditTimestamp: 78492,
         content: "<p>Hello, world</p>");
-      final messageList = await messageListViewWithMessages([originalMessage], store, narrow);
+      final messageList = await messageListViewWithMessages([originalMessage], stream, narrow);
 
       final updateEvent = UpdateMessageEvent(
         id: 1,