Revert "xdgmime: plug a small leak"

This reverts commit 4e7031f073.

The string actually does get freed somewhere else, at least in some
cases. Can be looked at again later if this reintroduces a leak.

https://bugzilla.gnome.org/show_bug.cgi?id=683270

gio/xdgmime/xdgmime.c

@@ -156,7 +156,6 @@ xdg_mime_init_from_directory (const char *directory)
           _caches[n_caches + 1] = NULL;
 	  n_caches++;
 
-          free (file_name);
 	  return FALSE;
 	}
     }