[TASK] Remove DH $overrideValues and overrideFieldArray()

This `@internal` property and method is another "has
never been used" detail: It dates back to very early
TYPO3 versions and TER reveals not a single usage.

In case there are still extensions dealing with that
public property, it should be possible to use hook
'processDatamap_postProcessFieldArray' instead, which
is dispatched within process_datamap() a couple of
lines later.

Resolves: #103137
Releases: main
Change-Id: If849f3f36aa160f8c467907b338aed27c7ef94eb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83020


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>