I've long considered the XMPP support in git-annex a wart.
It's nice to remove it.
(This also removes the NetMessager, which was only used for XMPP, and the
daemonstatus's desynced list (likewise).)
Existing XMPP remotes should be ignored by git-annex.
This commit was sponsored by Brock Spratlen on Patreon.