Remove dead code in rpc_parse.c

It's been dead ever since it was imported from TI-RPC in 1995. The dead
code is still present in Illumos today, but was removed from NetBSD in 2006.

Reported by: Coverity
CID: 270097
Obtained from: NetBSD
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp