use P2P protocol for checkpresent, retrieve, and store

Note that, due to not using rsync to transfer files to ssh remotes
any longer, permissions and other file metadata of annexed files
will no longer be preserved when copying them to ssh remotes.
Other remotes never supported preserving that information, so
this is not considered a regression. Added NEWS item about this.

Another significant side effect of this is that, even when rsync is run to
retrieve a file, its progress display will no longer be shown, and
instead the native git-annex progress display will appear. It would be
possible to use the rsync process display when rsync is used (old
git-annex-shell and also retrieval from a local repository), but it
would have complicated the code unncessarily, and been inconsistent
behavior.

(I'd been thinking for a while about eliminating the rsync progress
display, since it's got some annoying verbosities, including display of
the key and the "(xfr#1, to-chk=0/1)" bit and was already somewhat
inconsistent.)

retrieveKeyFileCheap still uses rsync, since that ensures that it gets
the actual file content from the remote. Using the P2P protocol would
use the local content, as long as the local and remote size are the
same.

This commit was sponsored by John Pellman on Patreon.

Messages/Progress.hs

@@ -77,15 +77,6 @@ metered othermeter key getsrcfile a = withMessageState $ \st ->
 				Nothing -> return Nothing
 				Just f -> catchMaybeIO $ liftIO $ getFileSize f
 
-{- Use when the command's own progress output is preferred.
- - The command's output will be suppressed and git-annex's progress meter
- - used for concurrent output, and json progress. -}
-commandMetered :: Maybe MeterUpdate -> Key -> Annex (Maybe FilePath) -> (MeterUpdate -> Annex a) -> Annex a
-commandMetered combinemeterupdate key getsrcfile a = 
-	withMessageState $ \s -> if needOutputMeter s
-		then metered combinemeterupdate key getsrcfile a
-		else a (fromMaybe nullMeterUpdate combinemeterupdate)
-
 {- Poll file size to display meter, but only when concurrent output or
  - json progress needs the information. -}
 meteredFile :: FilePath -> Maybe MeterUpdate -> Key -> Annex a -> Annex a