Revert "flush stream after each write to update-index, to possibly avoid buffering issues on Windows"

Didn't help.

Git/UpdateIndex.hs

@@ -44,7 +44,6 @@ streamUpdateIndex repo as = pipeWrite params repo $ \h -> do
 	streamer h s = do
 		hPutStr h s
 		hPutStr h "\0"
-		hFlush h
 
 {- A streamer that adds the current tree for a ref. Useful for eg, copying
  - and modifying branches. -}