No other sub directory provides such a configuration option, so
drop it from the sim dir as well. This cleans up a good bit of
code in the process.
If people want to use custom flags for just the sim, they can
still run configure+make by hand in the sim subdir and use the
normal CFLAGS settings.
The compiler/C library should produce reasonable code for htonl/ntohl,
and at least glibc tries pretty hard to always produce good code for
them. This logic only had support for 32-bit x86 systems anymore, and
it's unlikely people were even opting into this, so drop it all.
