Don't autoload new dns-mode command

* lisp/textmodes/dns-mode.el (dns-mode-ipv6-to-nibbles):
Remove autoload cookie.

lisp/textmodes/dns-mode.el

@@ -256,7 +256,6 @@ This function is run from `before-save-hook'."
 	   ;; We return nil in case this is used in write-contents-functions.
 	   nil)))
 
-;;;###autoload
 (defun dns-mode-ipv6-to-nibbles (&optional negate-prefix)
   "Convert an IPv6 address around or before point.
 Replace the address by its ip6.arpa-representation for use in