fdo#81787 attrs are already XML-encoded by libodfgen

Change-Id: Icee62e1ec9cee71930bcd52dbab850396fc96efa
(cherry picked from commit 46f52010e08ebc03c8a8efacd887b0ab526efaed)
Reviewed-on: https://gerrit.libreoffice.org/10901
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>