Fix EZP-22404: Fatal error in TransformationProcessor

JIRA: https://jira.ez.no/browse/EZP-22404

TransformationProcessors append the resources path to kernel root dir, so the changes introduced in PR #703 / #712 appear to be unnecessary and actually introduce a regression.
( the resulting path is ```/var/www/html/ezp/ezpublish//var/www/html/ezp/ezpublish/../vendor/ezsystems``` ... )

Ref:
* https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Publish/Core/Persistence/TransformationProcessor/PreprocessedBased.php#L52
* https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Publish/Core/Persistence/TransformationProcessor/DefinitionBased/Parser.php#L103