deskutils/caja-extensions: Drop (G)UPnP support

All available versions of caja-extensions depends on legacy version
of GUPnP which is unsupported upstream and doesn't build with newer
versions of libxml2. Drop plugin for new until it's fixed upstream.

gtk-doc is now a build dependency due to
https://savannah.gnu.org/support/?110503

Reference:
https://github.com/mate-desktop/caja-extensions/issues/110

PR: 273430
Approved by: portmgr (maintainer timeout, 2+ weeks)
Sponsored by: Blinkinblox