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

Change-Id: Iac5873a89af9a5ad395fae83fa2b2a10e706009a
Reviewed-on: http://review.typo3.org/35459
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>