[TASK] Remove Comment for deprecation of f:translate key

In future versions the usage of f:translate key and f:translate id
will both be possible, so the comment about a deprecation is removed.

Change-Id: I71a2fc1e9abec6b26c8b3848dd31e234fc056699
Fixes: #49670
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/21902
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring