java: remove some unused fields and variables

Change-Id: I5d6071096307adbe7df0178000346cf915afa3e7
Reviewed-on: https://gerrit.libreoffice.org/13477
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>