[TASK] SYS/forceReturnPath can be removed

Silent upgrader removes this setting now as well.

Resolves: #52857
Releases: 6.2
Change-Id: I03c5f302cce96f53a5664a1fafcd1c2d7b8ec812
Reviewed-on: https://review.typo3.org/24811
Reviewed-by: Alexander Stehlik
Tested-by: Alexander Stehlik
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters