Mark xml_parser_free as deprecated. (#4892)

* Mark xml_parser_free as deprecated.

* Flesh out deprecation markers further.

* Add formal warning.

* Remove redundant text.

Co-authored-by: Tim Düsterhus <timwolla@googlemail.com>

---------

Co-authored-by: Tim Düsterhus <timwolla@googlemail.com>

Author: Crell

reference/xml/functions/xml-parser-free.xml

@@ -66,6 +66,12 @@
      </row>
     </thead>
     <tbody>
+     <row>
+      <entry>8.5.0</entry>
+      <entry>
+       This function has been deprecated.
+      </entry>
+     </row>
       &xml.changelog.parser-param;
     </tbody>
    </tgroup>