Make `dired-split' obsolete

* lisp/dired-aux.el (dired-tree-lessp): Adjust caller.
(dired-split): Make obsolete (bug#50572).

* lisp/ffap.el (ffap-list-env): Adjust comment.

lisp/dired-aux.el

@@ -2860,8 +2860,8 @@ of marked files.  If KILL-ROOT is non-nil, kill DIRNAME as well."
   ;;   if dired-actual-switches contained t.
   (setq dir1 (file-name-as-directory dir1)
 	dir2 (file-name-as-directory dir2))
-  (let ((components-1 (dired-split "/" dir1))
-	(components-2 (dired-split "/" dir2)))
+  (let ((components-1 (split-string dir1 "/"))
+	(components-2 (split-string dir2 "/")))
     (while (and components-1
 		components-2
 		(equal (car components-1) (car components-2)))
@@ -2880,7 +2880,6 @@ of marked files.  If KILL-ROOT is non-nil, kill DIRNAME as well."
 	     nil)
 	    (t (error "This can't happen"))))))
 
-;; There should be a builtin split function - inverse to mapconcat.
 (defun dired-split (pat str &optional limit)
   "Splitting on regexp PAT, turn string STR into a list of substrings.
 Optional third arg LIMIT (>= 1) is a limit to the length of the
@@ -2890,6 +2889,7 @@ Thus, if SEP is a regexp that only matches itself,
    (mapconcat #'identity (dired-split SEP STRING) SEP)
 
 is always equal to STRING."
+  (declare (obsolete split-string "29.1"))
   (let* ((start (string-match pat str))
 	 (result (list (substring str 0 start)))
 	 (count 1)

lisp/ffap.el

@@ -651,7 +651,7 @@ also is substituted for the first empty-string component, if there is one.
 Uses `path-separator' to separate the path into substrings."
   ;; We cannot use parse-colon-path (files.el), since it kills
   ;; "//" entries using file-name-as-directory.
-  ;; Similar: dired-split, TeX-split-string, and RHOGEE's psg-list-env
+  ;; Similar: TeX-split-string, and RHOGEE's psg-list-env
   ;; in ff-paths and bib-cite.  The EMPTY arg may help mimic kpathsea.
   (if (or empty (getenv env))		; should return something
       (let ((start 0) match dir ret)