refactor(discover): 优化房间控制器逻辑

- 移除冗余的isLoading状态变量
- 简化RTC频道加入流程，移除重复调用
- 提升代码可读性和维护性

lib/controller/discover/room_controller.dart

@@ -19,9 +19,6 @@ class RoomController extends GetxController {
   /// 当前频道信息
   final Rxn<RtcChannelData> rtcChannel = Rxn<RtcChannelData>();
 
-  /// 是否正在创建
-  final RxBool isLoading = false.obs;
-
   /// 聊天消息列表
   final RxList<LiveChatMessage> chatMessages = <LiveChatMessage>[].obs;
 
@@ -88,7 +85,6 @@ class RoomController extends GetxController {
       if (base.isSuccess && base.data != null) {
         rtcChannel.value = base.data;
         await _joinRtcChannel(base.data!.token, base.data!.channelId, base.data!.uid, ClientRoleType.clientRoleBroadcaster);
-        await _joinRtcChannel(base.data!.token, base.data!.channelId, base.data!.uid);
       } else {
         final message = base.message.isNotEmpty ? base.message : '创建频道失败';
         SmartDialog.showToast(message);