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

Change-Id: Iebd043f85780941d0dce86e98497762bb4c0cf03
Reviewed-on: http://review.typo3.org/35457
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>