nodeinfo: remove FreeBSD specific code for getting memory
    
    The GNULIB physmem module already provides support for
    the FreeBSD platform, so there's no reason to re-implement
    FreeBSD portability code in libvirt. If there are bugs in
    the GNULIB code, we should fix GNULIB rather than workaround
    it in libvirt.
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>