pnmnoraw was replaced in Netpbm 8.2 (March 2000) by pnmtoplainpnm, which was obsoleted by pnmtopnm in Netpbm 10.23 (July 2004).
pnmtoplainpnm was actually the same program; it was just renamed to make it clear that is just a format converter.
pnmtopnm is more general, in that it can go both directions. pnmtopnm -plain is the same as pnmnoraw.