[TASK] Remove image map code from GifBuilder

While public, the addToMap method only filled a
protected property without an accessor, so while
a image map exists, it is never used in GifBuilder
or outside of it, warranting the removal of useless
functionality.

Resolves: #101973
Releases: main
Change-Id: If375d5060b966054698012eb97153121d31f9385
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81104


Tested-by: Andreas Nedbal <andy@pixelde.su>
Reviewed-by: Andreas Nedbal <andy@pixelde.su>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>