Remove all deprecated methods / props

src/structures/GroupDMChannel.js

@@ -155,11 +155,6 @@ class GroupDMChannel extends Channel {
   // These are here only for documentation purposes - they are implemented by TextBasedChannel
   /* eslint-disable no-empty-function */
   send() {}
-  sendMessage() {}
-  sendEmbed() {}
-  sendFile() {}
-  sendFiles() {}
-  sendCode() {}
   fetchMessage() {}
   fetchMessages() {}
   fetchPinnedMessages() {}