Remove dead links

Both of those URLs are unreachable. docs.indymedia.org doesn't show the
content and the wiki page on wiki.koumbit.net is set to private.

operator.md

-Notice: this was copied from https://docs.indymedia.org/Sysadmin/IrcOper and may be out of date. It also overlaps with Koumbit's documentation at https://wiki.koumbit.net/IrcMaintenance.
-
 See also http://www.stack.nl/~jilles/irc/charybdis-oper-guide/index.html
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