javaunohelper: remove unused import

Change-Id: Ibee790a50e35219a8427b7037331943b778292a2
Reviewed-on: https://gerrit.libreoffice.org/11997
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>