ox-koma-letter.el: No default opening and closing line.

	* ox-koma-letter.el (org-koma-letter-opening): No default / set to nil.
	(org-koma-letter-closing): No default / set to nil.

	We should not assume a formal English opening and closing
	line.  A letter requires many personal options, such as the
	address, so it is no more work to also these options.

TINYCHANGE

Signed-off-by: Alan Schmitt <alan.schmitt@polytechnique.org>

contrib/lisp/ox-koma-letter.el

@@ -105,12 +105,12 @@
   :group 'org-export-koma-letter
   :type 'string)
 
-(defcustom org-koma-letter-opening "Dear Madam or Sir,"
+(defcustom org-koma-letter-opening nil
   "Letter's opening, as a string."
   :group 'org-export-koma-letter
   :type 'string)
 
-(defcustom org-koma-letter-closing "Sincerely yours,"
+(defcustom org-koma-letter-closing nil
   "Koma-Letter's closing, as a string."
   :group 'org-export-koma-letter
   :type 'string)