[TASK] Remove unnecessary t3skin icon override settings

EXT:t3skin overrides some TCA icons which
can now be set directly, so the hacks for the old icon
API are not necessary anymore.

Resolves: #72577
Releases: master
Change-Id: Id21076d07f059b8203284bafecabce738c0f0a4f
Reviewed-on: https://review.typo3.org/45665


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>