javaunohelper: fix javadoc error: unknown tag: attention (Doxygen)

Change-Id: Idd1d92699cab0ccb26b95e9d5392c6fc7a8a2aa6
Reviewed-on: https://gerrit.libreoffice.org/11308
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>