finish message serialization of progress meters

Any given transfer can only display 1 progress meter at a time, or so
this code assumes. In some cases, there are progress meters for
different stages of a transfer, perhaps, and that is supported by this.

This commit was sponsored by Ethan Aubin.

Messages/Internal.hs

@@ -96,18 +96,3 @@ flushed a = a >> hFlush stdout
 
 outputSerialized :: (SerializedOutput -> IO ()) -> SerializedOutput -> IO ()
 outputSerialized = id
-
-emitSerializedOutput :: SerializedOutput -> Annex ()
-emitSerializedOutput (OutputMessage msg) =
-	outputMessage' nojsonoutputter nojsonbuilder msg
-  where
-	nojsonoutputter _ _ = return False
-	nojsonbuilder = id
-emitSerializedOutput (OutputError msg) = outputError msg
-emitSerializedOutput (ProgressMeter sz old new) = undefined -- TODO
-emitSerializedOutput (JSONObject b) =
-	withMessageState $ \s -> case outputType s of
-		JSONOutput _ -> liftIO $ flushed $ JSON.emit' b
-		SerializedOutput h -> liftIO $
-			outputSerialized h $ JSONObject b
-		_ -> q