Remove unecessary function call file-name-directory

Why:
It is called inside of the `idris-ipkg-buffer-src-dir` function.

Author: keram

idris-ipkg-mode.el

@@ -135,7 +135,7 @@
   "Make all modules with existing files clickable, where clicking opens them."
   (interactive)
   (idris-clear-file-link-overlays 'idris-ipkg-mode)
-  (let ((src-dir (idris-ipkg-buffer-src-dir (file-name-directory (buffer-file-name)))))
+  (let ((src-dir (idris-ipkg-buffer-src-dir (buffer-file-name))))
     ;; Make the sourcedir clickable
     (when (and (file-exists-p src-dir)
                (file-directory-p src-dir)