Breaking: #101398 - Remove leftover $fetchAllFields in RelationHandler 

See forge#101398

Description 

The \TYPO3\CMS\Core\Database\RelationHandler had an unused property $fetchAllFields since TYPO3 v11.5.0. The related method setFetchAllFields() has been removed with it.

Impact 

Custom extensions calling \TYPO3\CMS\Core\Database\RelationHandler->setFetchAllFields() will result in a PHP Fatal error.

Affected installations 

All installations with custom extensions calling \TYPO3\CMS\Core\Database\RelationHandler->setFetchAllFields().

Migration 

Remove the affected line of code. This method has had no effect since TYPO3 v11.5.0.