Backport commit bd60fca2f from Emacs

* lisp/ox-koma-letter.el (org-koma-letter-export-block)
(org-koma-letter-export-snippet): Fix warning about two unused
parameter.

Fix ox-koma-letter compilation warnings
bd60fca2faa03034e89df68a69255656df6512ba
Lars Ingebrigtsen
Sat Oct 2 10:37:55 2021 +0200

[ km: This has already been taken care of in the bugfix branch by
  85e5540eb (lisp/ox-koma-letter.el: Use lexical-binding,
  2021-09-30). ]

lisp/ox-koma-letter.el

@@ -594,7 +594,7 @@ such as the one tagged with PS."
 
 ;;;; Export Block
 
-(defun org-koma-letter-export-block (export-block contents info)
+(defun org-koma-letter-export-block (export-block _contents _info)
   "Transcode an EXPORT-BLOCK element into KOMA Scrlttr2 code.
 CONTENTS is nil.  INFO is a plist used as a communication
 channel."
@@ -604,7 +604,7 @@ channel."
 
 ;;;; Export Snippet
 
-(defun org-koma-letter-export-snippet (export-snippet contents info)
+(defun org-koma-letter-export-snippet (export-snippet _contents _info)
   "Transcode an EXPORT-SNIPPET object into KOMA Scrlttr2 code.
 CONTENTS is nil.  INFO is a plist used as a communication
 channel."