[BUGFIX] Remove wrong label in backend

Since 1.7 powermail forms are not saved automatically anymore. This
patches removes the wrong label add on for the German translation.

Change-Id: I50137d7365aded3178ddffc83683203a983eb20d
Reviewed-on: https://review.typo3.org/25217
Reviewed-by: Nicole Cordes
Tested-by: Nicole Cordes