CTCP commands other than ACTION are designed for client-to-client interaction on
IRC networks. Drop such messages when we receive them.
Also get rid of a "CTCP_ACTION" handler in the handler registration.
This
1) can't do anything (if anything, we wanted the string constant
girc.CTCP_ACTION, which is "ACTION")
2) doesn't do anything in this context, because CTCP handlers are
registered separately:
f47717952b/ctcp.go (L205)
The PRIVMSG handler already listens to all CTCPs.
Thanks to @lexande for the bug report (found on a live instance).
0bb521512a