Anyway, I can not imagine any scenario where removing external links would
make any sense. Can you tell us why you want to cripple the wiki that way?
We are using dokuwiki as an intranet wiki at my company and if someone
adds an external link, it will send referrer information containing
the current page name to the destination site.
The names of some of the pages could leak confidential information.
We do have a policy prohibiting it, but that has not stopped the
occasional slip-up.