java: the TempFileTest interface is unnecessary

Change-Id: Ic49f95117b54929f95984aff0f69e47b90daee7c
Reviewed-on: https://gerrit.libreoffice.org/13404
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>