[PATCH] Don't add nis subdir for new architectures

[Florian Weimer]

* Andreas Schwab:

> For future architectures, sysdeps/unix/inet no longer implies building the
> nis subdirectory, and --enable-obsolete-nsl is ignored.

I think we should remove --enable-obsolete-rpc and
--enable-obsolete-nsl altogether, and no longer include the compat
symbols for new architectures, as usual.