[CLEANUP] #5206 Drop the unset from tearDown()

Change-Id: Id5f1a20269125c1df8f481bedbf31b638c60c919
Reviewed-on: http://review.typo3.org/35458
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>