chore(tests): remove unused import from external_asset_handler_test.dart

Author: dgarciasquare1

test/utils/external_asset_handler_test.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter_policy_engine/src/utils/external_asset_handler.dart';
-import 'package:flutter_policy_engine/src/utils/json_handler.dart';
 import 'package:flutter_policy_engine/src/utils/log_handler.dart';
 
 void main() {