libvirt: Remove defunct comment
libvirt: Remove defunct comment

This comment hasn't applied since Ifea7f9f61ad9fd1a5e1995074790ec4ab63fd0ed
when this code was moved.

Change-Id: I29171f8e0b5b37c4a817b08f3dad4099f21cdc8a

mahak/nova,mahak/nova,openstack/nova,mahak/nova,openstack/nova,openstack/nova