Fix lint issue

lib/src/ui/keyboard_visibility.dart

@@ -1,5 +1,3 @@
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 class KeyboardVisibilty extends StatefulWidget {

lib/src/ui/shortcut/actions.dart

@@ -1,7 +1,5 @@
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
-import 'package:xterm/src/core/buffer/cell_offset.dart';
-import 'package:xterm/src/core/buffer/range_line.dart';
 import 'package:xterm/src/terminal.dart';
 import 'package:xterm/src/ui/controller.dart';
 import 'package:xterm/src/ui/selection_mode.dart';