sunrpc: Remove stray exports without --enable-obsolete-rpc [BZ #23166]

This is needed to avoid a warning when linking against libtirpc:

/lib64/libc.so.6: warning: common of `rpc_createerr@@TIRPC_0.3.0' overridden by definition
/usr/lib64/libtirpc.so: warning: defined here

This ld warning is not enabled by default; -Wl,--warn-common enables it.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>