Clean up the stuff we do to get <inttypes.h> stuff defined.

Clean up the stuff we do to get <inttypes.h> stuff defined.

If we have a libpcap with <pcap/pcap-inttypes.h>, include it, so that we
don't have to worry about definitions colliding if we later include a
pcap header file that includes pcap/pcap-inttypes.h.

Otherwise, do the same stuff pcap-inttypes.h does.  This means that, on
UN*X, we require that there be an <inttypes.h> that defines everything
we need.

Don't bother doing checks that are no longer necessary as a result of
those changes.