mu4e: clean up some unneeded backports

Remove some functions we no longer need with Emacs 28.

There's still some things left, which will be handled in due time.

mu4e/mu4e-helpers.el

@@ -583,12 +583,6 @@ COMPONENTS."
    (mapconcat (lambda (part) (if (stringp part) part ""))
               (cons directory components) "/")))
 
-(defun mu4e-string-replace (from-string to-string in-string)
-  "Replace FROM-STRING with TO-STRING in IN-STRING each time it occurs.
-Mu4e's version of Emacs 28's `string-replace'."
-  (replace-regexp-in-string (regexp-quote from-string)
-                            to-string in-string nil 'literal))
-
 (defun mu4e-plistp (object)
   "Non-nil if and only if OBJECT is a valid plist.
 This is mu4e's version of Emacs 29's `plistp'."

mu4e/mu4e-main.el

@@ -203,10 +203,10 @@ binding representation, remove that first letter."
          (bindstr
           (if (and alt (> (length bindstr) 1)) alt bindstr))
          (title ;; remove first letter afrer [] if it equal last of binding
-          (mu4e-string-replace
+          (string-replace
            (concat "[@]" (substring bindstr -1)) "[@]" title))
          (title ;; insert binding in [@]
-          (mu4e-string-replace
+          (string-replace
            "[@]" (format "[%s]" (propertize bindstr 'face 'mu4e-highlight-face))
            title))
          (map (make-sparse-keymap)))

mu4e/mu4e-obsolete.el

@@ -1,6 +1,6 @@
 ;;; mu4e-obsolete.el --- Obsolete things -*- lexical-binding: t -*-
 
-;; Copyright (C) 2022-2024 Dirk-Jan C. Binnema
+;; Copyright (C) 2022-2026 Dirk-Jan C. Binnema
 
 ;; Author: Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 ;; Maintainer: Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
@@ -283,5 +283,7 @@
 ;; mu4e.
 (define-obsolete-function-alias 'mu4e-clear-caches #'ignore "1.11.15")
 
+(define-obsolete-function-alias 'mu4e-string-replace #'string-replace "1.14.0")
+
 (provide 'mu4e-obsolete)
 ;;; mu4e-obsolete.el ends here