Remove the last leftovers from IA64 Xen pv-guest support.

PARAVIRT is long gone from IA64 Kconfig and Xen IA64 support, too.

Due to lack of infrastructure no testing done.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20191021100415.7642-1-jgross@suse.com