Cleanup: remove the old FIO slot functions

(cherry picked from commit fa6abe1646)

src/openttd.cpp

@@ -445,9 +445,6 @@ static void ShutdownGame()
 	/* No NewGRFs were loaded when it was still bootstrapping. */
 	if (_game_mode != GM_BOOTSTRAP) ResetNewGRFData();
 
-	/* Close all and any open filehandles */
-	FioCloseAll();
-
 	UninitFreeType();
 
 	ViewportMapClearTunnelCache();