remove useless native code

lib/src/message_input.dart

@@ -664,6 +664,7 @@ class MessageInputState extends State<MessageInput> {
                   Navigator.pop(context);
                 },
               ),
+              if (!kIsWeb)
                 ListTile(
                   leading: Icon(Icons.camera_alt),
                   title: Text('Photo from camera'),
@@ -672,6 +673,7 @@ class MessageInputState extends State<MessageInput> {
                     Navigator.pop(context);
                   },
                 ),
+              if (!kIsWeb)
                 ListTile(
                   leading: Icon(Icons.videocam),
                   title: Text('Video from camera'),
@@ -943,6 +945,7 @@ class MessageInputState extends State<MessageInput> {
   void initState() {
     super.initState();
 
+    if (!kIsWeb) {
       _keyboardListener = KeyboardVisibility.onChange.listen((visible) {
         if (visible) {
           if (_commandsOverlay != null) {
@@ -971,6 +974,7 @@ class MessageInputState extends State<MessageInput> {
           }
         }
       });
+    }
 
     textEditingController =
         widget.textEditingController ?? TextEditingController();
@@ -997,7 +1001,7 @@ class MessageInputState extends State<MessageInput> {
   void dispose() {
     _commandsOverlay?.remove();
     _mentionsOverlay?.remove();
-    _keyboardListener.cancel();
+    _keyboardListener?.cancel();
     super.dispose();
   }