chore: delete unused import

frontend/app_flowy/packages/flowy_editor/example/lib/plugin/text_node_widget.dart

@@ -2,7 +2,6 @@ import 'package:flowy_editor/document/text_delta.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flowy_editor/flowy_editor.dart';
-import 'package:flowy_editor/operation/transaction_builder.dart';
 import 'package:flutter/services.dart';
 import 'package:flowy_editor/document/attributes.dart';