[!!!][TASK] Remove setting 'GFX/processor_allowTemporaryMasksAsPng'

This setting stems from an even older setting called
'im_mask_temp_ext_gif' which was introduced because of
issues with PNG file generation with some earlier
versions of ImageMagick 5.

TYPO3 requires at least ImageMagick 6 or newer in recent
versions, where PNG generation issues couldn't be observed
using this setting. It's obsolete and removed.

Resolves: #101950
Releases: main
Change-Id: I4d6fd01591c1f36fe22e4019392ffdab2be908a9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81084


Tested-by: Andreas Nedbal <andy@pixelde.su>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Nedbal <andy@pixelde.su>
Tested-by: Benni Mack <benni@typo3.org>