Somewhat sped up git commit of modifications to unlocked files.

Avoid git reset here too, so I no longer need to care that it's much more
expensive than seems wise (but I asked the git list about that anyway).

It's not necessary to reset the staged file content from the index, as
the `git add` of the the symlink will replace it anyway.

`git commit` of unlocked files is still slow, since git still has to shove
their entire content into the index, only to have it be thrown away. So it's
still better to use `git annex add`

Command/PreCommit.hs

@@ -33,15 +33,5 @@ perform :: BackendFile -> CommandPerform
 perform pair@(file, _) = do
 	ok <- doCommand $ Command.Add.start pair
 	if ok
-		then next $ cleanup file
+		then next $ return True
 		else error $ "failed to add " ++ file ++ "; canceling commit"
-
-cleanup :: FilePath -> CommandCleanup
-cleanup file = do
-	-- git commit will have staged the file's content;
-	-- drop that and run command queued by Add.state to
-	-- stage the symlink
-	g <- Annex.gitRepo
-	liftIO $ Git.run g "reset" [Params "-q --", File file]
-	AnnexQueue.flush True
-	return True