Currently the scheduler depends at many parts on its classname field in
the tx_scheduler_task table. This is not necessary as the classname is
already stored in the serialized task object. By releasing scheduler
tasks from their classname field backwards compatibility is maintained
by the class_alias mechanism.

Change-Id: I26f228add1f3db9f99ec3f5691488bd453ae2339
Fixes: #40215
Related: #40095
Releases: 6.0
Reviewed-on: http://review.typo3.org/14236
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert