Remove %BSD.reds and put the MacOSX definition in %darwin.reds.

We could probably have a common %BSD.reds for the other *BSDs even
if some of their structures and siginfo codes differ. MacOSX is
different enough that it makes sense to split it out.

The non MacOSX signal handling code didn't work so I removed it.
Add FreeBSD signal handling and initialization to %freebsd.reds.