HA Guide: Fix XML header
HA Guide: Fix XML header

Do not set xml:lang and add xlink namespace.

Change-Id: I9fd243a0e2ab5c545262bf2ca3be11ee079c89e6

openstack/openstack-manuals,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,gongysh2004/openstack-manual,potsmaster/openstack-manuals,saeki-masaki/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,gongysh2004/openstack-manual,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,potsmaster/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals