ox-html.el (org-html-protect-char-alist): Make a defvar

* ox-html.el (org-html-protect-char-alist): Make a defvar.

lisp/ox-html.el

@@ -790,14 +790,11 @@ link's path."
 
 ;;;; Plain Text
 
-(defcustom org-html-protect-char-alist
+(defvar org-html-protect-char-alist
   '(("&" . "&")
     ("<" . "&lt;")
     (">" . "&gt;"))
-  "Alist of characters to be converted by `org-html-protect'."
-  :group 'org-export-html
-  :type '(repeat (cons (string :tag "Character")
-		       (string :tag "HTML equivalent"))))
+  "Alist of characters to be converted by `org-html-protect'.")
 
 ;;;; Src Block