org-compat: Remove `org-decode-time'

* lisp/org-compat.el (org-decode-time): Remove compatibility function,
  no longer used.

lisp/org-compat.el

@@ -61,12 +61,6 @@
   (defalias 'format-message 'format)
   (defalias 'gui-get-selection 'x-get-selection))
 
-(defun org-decode-time (&optional time zone)
-  "Backward-compatible function for `decode-time'."
-  (if (< emacs-major-version 25)
-      (decode-time time)
-    (decode-time time zone)))
-
 (unless (fboundp 'directory-name-p)
   (defun directory-name-p (name)
     "Return non-nil if NAME ends with a directory separator character."