javaunohelper: The assigned value is never used

Change-Id: Ia190a6784fceaf9607ba39f2ef9d5ea4151cfc16
Reviewed-on: https://gerrit.libreoffice.org/10624
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>