remove xmpp support

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.

Command/XMPPGit.hs

@@ -1,48 +0,0 @@
-{- git-annex command
- -
- - Copyright 2012 Joey Hess <id@joeyh.name>
- -
- - Licensed under the GNU GPL version 3 or higher.
- -}
-
-module Command.XMPPGit where
-
-import Command
-import Assistant.XMPP.Git
-
-cmd :: Command
-cmd = noCommit $ dontCheck repoExists $
-	noRepo (parseparams startNoRepo) $ 
-		command "xmppgit" SectionPlumbing "git to XMPP relay"
-			paramNothing (parseparams seek)
-  where
-	parseparams = withParams
-
-seek :: CmdParams -> CommandSeek
-seek = withWords start
-
-start :: CmdParams -> CommandStart
-start _ = do
-	liftIO gitRemoteHelper
-	liftIO xmppGitRelay
-	stop
-
-startNoRepo :: CmdParams -> IO ()
-startNoRepo _ = xmppGitRelay
-
-{- A basic implementation of the git-remote-helpers protocol. -}
-gitRemoteHelper :: IO ()
-gitRemoteHelper = do
-	expect "capabilities"
-	respond ["connect"]
-	expect "connect git-receive-pack"
-	respond []
-  where
-	expect s = do
-		gitcmd <- getLine
-		unless (gitcmd == s) $
-			error $ "git-remote-helpers protocol error: expected: " ++ s ++ ", but got: " ++ gitcmd
-	respond l = do
-		mapM_ putStrLn l
-		putStrLn ""
-		hFlush stdout