get rid of racy addLink

The remaining callers all did not rely on it checking gitignore, so were
easy to convert.

They were susceptable to the same overwrite race as add and fix,
although less likely to have it and a narrower window than add's race.

Command.Rekey in passing got an unncessary call to removeFile deleted.
addSymlink handles deleting any existing worktree file.

Command/ReKey.hs

@@ -123,8 +123,7 @@ cleanup file newkey = do
 	ifM (isJust <$> isAnnexLink file)
 		( do
 			-- Update symlink to use the new key.
-			liftIO $ removeFile (fromRawFilePath file)
-			addLink (CheckGitIgnore False) file newkey Nothing
+			addSymlink file newkey Nothing
 		, do
 			mode <- liftIO $ catchMaybeIO $ fileMode <$> R.getFileStatus file
 			liftIO $ whenM (isJust <$> isPointerFile file) $