Revert "Revert "Revert "Use `xdg-open' to open files where available"""

This reverts commit 0022904e83babacbdbaf167fcbf488dbf90dd78e.

lisp/org.el

@@ -1899,13 +1899,9 @@ single keystroke rather than having to type \"yes\"."
   :type 'regexp)
 
 (defconst org-file-apps-defaults-gnu
-  (append
-   '((remote . emacs))
-   (if (executable-find "xdg-open")
-       '((system . "xdg-open %s")
-	 (t . "xdg-open %s"))
-     '((system . mailcap)
-       (t . mailcap))))
+  '((remote . emacs)
+    (system . mailcap)
+    (t . mailcap))
   "Default file applications on a UNIX or GNU/Linux system.
 See `org-file-apps'.")