Update EntityReferenceHandler.php

Author: claudiu-cristea

src/Drupal/Driver/Fields/Drupal8/EntityReferenceHandler.php

@@ -41,8 +41,6 @@ class EntityReferenceHandler extends AbstractHandler {
   public function expand($values) {
     $this->targetEntityTypeId = $this->fieldInfo->getSetting('target_type');
 
-    $id_key = $entity_definition->getKey('id');
-
     // Determine label field key.
     if ($this->targetEntityTypeId !== 'user') {
       $this->targetLabelKey = $this->getEntityTypeKey($this->targetEntityTypeId, 'label');