xmpp: Remove unused prototypes and code
Review Request #1905 — Created Oct. 7, 2022 and submitted
Many functions are 'public' in that they are in header files, but they don't need to be. The
jabber.cones were likely there because of the xmpp/gtalk multi-library thing that's gone now.
This removal is 'naive', in that if a prototype is necessary for now-
staticfunctions, then that's all I did, instead of any re-ordering.
I also left in some 'unused'
data.cfunctions as their use was deleted when removing smileys and they may still be needed.