AGPL-3.0: Drop redundant release-date <notes>

The XSD suggests (buggily) that we only want a single <notes> element
(more details on this in 5010132, wxWindows: Collapse to a single
<notes> element, 2017-12-27, spdx#577).  And the information contained in
the <notes> section I'm removing is redundant, because the titleText
contains the release date.  I don't see a need to include that release
date as unstrucutured information in two places, and the license title
is clearly the more important location.

src/AGPL-3.0.xml

@@ -23,9 +23,6 @@
       along with this program. If not, see
       &lt;http<optional>s</optional>://www.gnu.org/licenses/&gt;
     </standardLicenseHeader>
-    <notes>
-      This version was released: 19 November 2007
-    </notes>
     <titleText>
       <p>
         GNU AFFERO GENERAL PUBLIC LICENSE<br></br>