java: merge JUnitBasedTest into DocumentEvents

since it was the only place that used it

Change-Id: If9a71fbb468d02616da5cfacab0332e51a416d13
Reviewed-on: https://gerrit.libreoffice.org/13407
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>