Looks like they're giving users of IRC clients the short end of the stick, and have started deprecating all that stuff. Because, hey, why send a simple IRC command to ban someone when you can do the same thing with half a dozen lines of JSON code sent through a socket!

https://discuss.dev.twitch.tv/t/deprecation-of-chat-commands-through-irc/40486
https://dev.twitch.tv/docs/irc/chat-commands/