Remove bugfix for imenu in Emacs 24.3 and below

This is no longer necessary, since we are dropping support for Emacs
24.3

Relates to: #26

lisp/pdf-outline.el

@@ -572,23 +572,6 @@ not call `imenu-sort-function'."
     (cons title
           (nconc (nreverse keep-at-top) menulist))))
 
-;; bugfix for imenu in Emacs 24.3 and below.
-(when (condition-case nil
-          (progn (imenu--truncate-items '(("" 0))) nil)
-        (error t))
-  (eval-after-load "imenu"
-    '(defun imenu--truncate-items (menulist)
-       "Truncate all strings in MENULIST to `imenu-max-item-length'."
-       (mapc (lambda (item)
-               ;; Truncate if necessary.
-               (when (and (numberp imenu-max-item-length)
-                          (> (length (car item)) imenu-max-item-length))
-                 (setcar item (substring (car item) 0 imenu-max-item-length)))
-               (when (imenu--subalist-p item)
-                 (imenu--truncate-items (cdr item))))
-             menulist))))
-
-
 
 (provide 'pdf-outline)