Add comment to check-rpc-mappings, clariying rpcnames.
Add comment to check-rpc-mappings, clariying rpcnames.

src/wallet/rpcnames.cpp is not listed in the array of source files to
scan in check-rpc-mappings, as it does not contain a dispatch table
itself.  Add a comment to make this clearer in the code.

namecoin/namecoin-core,namecoin/namecoin-core,domob1812/huntercore,domob1812/namecore,namecoin/namecoin-core,pataquets/namecoin-core,namecoin/namecore,namecoin/namecoin-core,pataquets/namecoin-core,domob1812/namecore,domob1812/namecore,namecoin/namecore,namecoin/namecore,domob1812/huntercore,namecoin/namecore,domob1812/huntercore,domob1812/namecore,pataquets/namecoin-core,domob1812/huntercore,namecoin/namecore,namecoin/namecoin-core,domob1812/namecore,pataquets/namecoin-core,pataquets/namecoin-core,domob1812/huntercore,domob1812/namecore,namecoin/namecore,pataquets/namecoin-core,domob1812/huntercore,namecoin/namecoin-core