The simpler interface (based on the BSD function) has been in libc since
Solaris 7, and avoids datasize bugs like the previous fix, so might as
well use it.

Purge all the other ancient Solaris & SunOS support variants as well.

This does mean if you want to keep running xload on a Sun OS version from
before 1998 you will need to use a branch of xload from before 2012 (such
as the one included in those old releases).

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>