java: remove some unnecessary interfaces

Change-Id: Ie2da7cbbd1733881ff2da6fa095c37c21cf19fe8
Reviewed-on: https://gerrit.libreoffice.org/13435
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>