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

Change-Id: Ie03f3b918fb5cd389490817544c650f6b775f2e7
Reviewed-on: http://review.typo3.org/35460
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>