[TASK] Remove unused DH $remapStackChildIds

In this episode of 'Cracking the Cryptic' we are
looking at the DataHandler puzzle ;)
Let's get some obvious things done, first:

Protected property DataHandler->remapStackChildIds
is only written but never read. Remove property
and protected addNewValuesToRemapStackChildIds()
with all its callers to reduce complexity a bit.

Resolves: #103132
Releases: main
Change-Id: I914ae36875906acc8e39799e640899116b3206ee
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83015


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>