Revert addition of 'callto' protocol in default recognized protocols.

Revert addition of 'callto' protocol in default recognized protocols.
I find this rather creepy; on clicking the link, Skype *immediately*
calls the named user. It looks like it may do the same for SkypeOut
numbers, which could be costly, annoying, as well as a privacy issue
if malicious linkers are trying to trick people into following the
links.

I can see this being useful for an intranet or other semiprivate
wiki, but that can then be added by the administrators of that
wiki.