Remove the variable oldname which is attempting to free stack space.

Historically this variable hold previous value of filename that
had to be freed if allocated previously. Currently this branch
is entered only if filename was not allocated previously so it
became redundant. It did not cause real problems because grub_free
was not called, but code is confusing and causes compilation error
in some cases.

grub-core/fs/iso9660.c

@@ -750,19 +750,15 @@ grub_iso9660_iterate_dir (grub_fshelp_node_t dir,
 
         if (dir->data->joliet && !ctx.filename)
           {
-            char *oldname, *semicolon;
+            char *semicolon;
 
-            oldname = name;
             ctx.filename = grub_iso9660_convert_string
-                  ((grub_uint8_t *) oldname, dirent.namelen >> 1);
+                  ((grub_uint8_t *) name, dirent.namelen >> 1);
 
 	    semicolon = grub_strrchr (ctx.filename, ';');
 	    if (semicolon)
 	      *semicolon = '\0';
 
-            if (ctx.filename_alloc)
-              grub_free (oldname);
-
             ctx.filename_alloc = 1;
           }