chore: remove unused ref

Author: appflowy

frontend/app_flowy/lib/plugins/board/presentation/toolbar/board_setting.dart

@@ -8,7 +8,6 @@ import 'package:appflowy_popover/popover.dart';
 import 'package:easy_localization/easy_localization.dart';
 import 'package:flowy_infra/image.dart';
 import 'package:flowy_infra/theme.dart';
-import 'package:flowy_infra_ui/flowy_infra_ui.dart';
 import 'package:flowy_infra_ui/style_widget/button.dart';
 import 'package:flowy_infra_ui/style_widget/scrolling/styled_list.dart';
 import 'package:flowy_infra_ui/style_widget/text.dart';