I think a grinder would be best or a file. I suppose you could use a dremel and a cut-off disk to knock the edges off. To do it faster you could put those screws in the drill and use some sand paper stapled to a block of wood, though I don't know how well the sand paper would hold up, a grinding stone would be better, but that would get you a pencil type sharpness...whatever you choose, just be careful and wear safety glasses.