docs: remove <auth> from secret XML format

This belongs to the pool definition.

docs/formatsecret.html.in

@@ -106,7 +106,6 @@
     <pre>
       &lt;secret ephemeral='no' private='yes'&gt;
          &lt;description&gt;CEPH passphrase example&lt;/description&gt;
-         &lt;auth type='ceph' username='myname'/&gt;
          &lt;usage type='ceph'&gt;
             &lt;name&gt;ceph_example&lt;/name&gt;
          &lt;/usage&gt;
@@ -192,7 +191,6 @@
     <pre>
       &lt;secret ephemeral='no' private='yes'&gt;
          &lt;description&gt;Passphrase for the iSCSI example.com server&lt;/description&gt;
-         &lt;auth type='chap' username='myname'/&gt;
          &lt;usage type='iscsi'&gt;
             &lt;target&gt;libvirtiscsi&lt;/target&gt;
          &lt;/usage&gt;