refactor!: finish parser migration

Finally! :)

This removes all code related to the old parser.

#65

lib/parser/classes/livechat/items/LiveChatViewerEngagementMessage.js

@@ -0,0 +1,20 @@
+'use strict';
+
+const LiveChatTextMessage = require('./LiveChatTextMessage');
+const Parser = require('../../..');
+
+class LiveChatViewerEngagementMessage extends LiveChatTextMessage {
+  type = 'LiveChatViewerEngagementMessage';
+
+  constructor(data) {
+    super(data);
+
+    delete this.author;
+    delete this.menu_endpoint;
+
+    this.icon_type = data.icon.iconType;
+    this.action_button = Parser.parse(data.actionButton);
+  }
+}
+
+module.exports = LiveChatViewerEngagementMessage;