Tweak comments in the policykit rules file

- Add the XML header so vim gives us syntax highlighting
- polkit-policy-file-validate hasn't existed for 3 years
- Permissions comment was not accurate

daemon/libvirtd.policy.in

+<?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE policyconfig PUBLIC
  "-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN"
  "http://www.freedesktop.org/standards/PolicyKit/1.0/policyconfig.dtd">
@@ -9,10 +10,6 @@ Copyright (c) 2007 Daniel P. Berrange <berrange redhat com>
 
 libvirt is licensed to you under the GNU Lesser General Public License
 version 2. See COPYING for details.
-
-NOTE: If you make changes to this file, make sure to validate the file
-using the polkit-policy-file-validate(1) tool. Changes made to this
-file are instantly applied.
 -->
 
 <policyconfig>
@@ -32,8 +29,8 @@ file are instantly applied.
       <description>Manage local virtualized systems</description>
       <message>System policy prevents management of local virtualized systems</message>
       <defaults>
-        <!-- Only a program in the active host session can use libvirt in
-             read-write mode for management, and we require user password -->
+        <!-- Any program can use libvirt in read/write mode if they
+             provide the root password -->
         <allow_any>auth_admin</allow_any>
         <allow_inactive>auth_admin</allow_inactive>
         <allow_active>@authaction@</allow_active>