[BUGFIX] Do not validate selectTree in SelectTreeElement.ts

The validation is already done in the FormEngineValidation on load.

In the method loadDataAfter the tree nodes are not yet loaded for
whatever reason and thus the validation always fails if having minitems
set.

Resolves: #94466
Releases: master
Change-Id: I47b0c3bcbb64887239ba30b1a56fbc5681072120
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/69731


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>