lisp/org.el: Make `org-toggle-link-display' more consistent

* lisp/org.el (org-do-emphasis-faces): Don't hide with `org-link'
as the value for the invisible text property.

Before this commit, M-x org-toggle-link-display RET would also toggle
the emphasis markers.

Reported-by: Gustavo Barros <gusbrs.2016@gmail.com>
Link: https://orgmode.org/list/87o8jnzjao.fsf@gmail.com/

lisp/org.el

@@ -5059,9 +5059,9 @@ stacked delimiters is N.  Escaping delimiters is not possible."
 	      (when (and org-hide-emphasis-markers
 			 (not (org-at-comment-p)))
 		(add-text-properties (match-end 4) (match-beginning 5)
-				     '(invisible org-link))
+				     '(invisible t))
 		(add-text-properties (match-beginning 3) (match-end 3)
-				     '(invisible org-link)))
+				     '(invisible t)))
 	      (throw :exit t))))))))
 
 (defun org-emphasize (&optional char)