xen: Drop XEN_DOMCTL_{get,set}_machine_address_size

xen: Drop XEN_DOMCTL_{get,set}_machine_address_size

This functionality is obsolete.  It was introduced by c/s 41296317a31 into
Xend, but was never exposed in libxl.

Nothing limits this to PV guests, but it makes no sense for HVM guests.

Looking through the XenServer templates, this was used to work around bugs in
the 32bit RHEL/CentOS 4.7 and 4.8 kernels (fixed in 4.9) and RHEL/CentOS/OEL
5.2 and 5.3 kernels (fixed in 5.4).  RHEL 4 as a major version went out of
support in 2017, whereas the 5.2/5.3 kernels went out of support when 5.4 was
released in 2009.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Acked-by: Wei Liu <wl@xen.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>