remove ability to join guilds

because 1. joining a guild seems to often require captchas now which are never going to be supported and 2. joining guilds is one of the things that upsets discords spam filter the most, so it kinda makes sense to remove anyways just like open dm

src/discord/discord.cpp

@@ -573,10 +573,6 @@ void DiscordClient::SendThreadLazyLoad(Snowflake id) {
     m_websocket.Send(msg);
 }
 
-void DiscordClient::JoinGuild(const std::string &code) {
-    m_http.MakePOST("/invites/" + code, "{}", [](auto) {});
-}
-
 void DiscordClient::LeaveGuild(Snowflake id) {
     m_http.MakeDELETE("/users/@me/guilds/" + std::to_string(id), [](auto) {});
 }