Refact. Flutter web, mid commit (#7494)

Signed-off-by: fufesou <shuanglongchen@yeah.net>

flutter/lib/models/server_model.dart

@@ -1,6 +1,5 @@
 import 'dart:async';
 import 'dart:convert';
-import 'dart:io';
 
 import 'package:flutter/material.dart';
 import 'package:flutter_hbb/consts.dart';
@@ -383,7 +382,7 @@ class ServerModel with ChangeNotifier {
     // ugly is here, because for desktop, below is useless
     await bind.mainStartService();
     updateClientState();
-    if (Platform.isAndroid) {
+    if (isAndroid) {
       WakelockPlus.enable();
     }
   }
@@ -395,7 +394,7 @@ class ServerModel with ChangeNotifier {
     await parent.target?.invokeMethod("stop_service");
     await bind.mainStopService();
     notifyListeners();
-    if (!Platform.isLinux) {
+    if (!isLinux) {
       // current linux is not supported
       WakelockPlus.disable();
     }