The coating is not anodizing, it is Fe3O4, black iron oxide. You should be able to remove it with a moderate strength acid. There is a product available at most hardware stores called 'Muriatic Acid', which is a ~30% hydrochloric acid solution. A few minutes of soaking should remove the black oxide coating, but be warned that the parts will begin to rust immediately afterward, so be sure to coat them with light oil after rinsing off the acid.