docs: undocument private constructors (#6732)

src/structures/DMChannel.js

@@ -10,10 +10,6 @@ const MessageManager = require('../managers/MessageManager');
  * @implements {TextBasedChannel}
  */
 class DMChannel extends Channel {
-  /**
-   * @param {Client} client The instantiating client
-   * @param {APIChannel} data The data for the DM channel
-   */
   constructor(client, data) {
     super(client, data);