[TASK] Signal/slot is available since TYPO3 4.6

Resolves: #61619
Change-Id: I47e32be3eab9afe04275d246e0a42b119358b554
Reviewed-on: http://review.typo3.org/32791
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>