Move clearing the target from the processor to the target plugin

Let's see if this breaks any tests.

+++ b/src/Feeds/Processor/EntityProcessorBase.php
@@ -1322,7 +1324,7 @@ abstract class EntityProcessorBase extends ProcessorBase implements EntityProces
-    unset($entity_target->{$target_name});
+    $target->clearTarget($feed, $entity_target, $target_name);

+++ b/src/Plugin/Type/Target/TargetBase.php
@@ -57,6 +59,13 @@ abstract class TargetBase extends PluginBase implements TargetInterface, PluginF
+  public function clearTarget(FeedInterface $feed, EntityInterface $entity, string $target) {
+    unset($entity->{$target});

Any reason to pass a feed object if it's unused?

Yes, it is for consistency with other methods in \Drupal\feeds\Plugin\Type\Target\TargetInterface, most notably setTarget() and isEmpty():

/**
 * Sets the values on an object.
 *
 * @param \Drupal\feeds\FeedInterface $feed
 *   The feed object.
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The target object.
 * @param string $target
 *   The name of the target to set.
 * @param array $values
 *   A list of values to set on the target.
 */
public function setTarget(FeedInterface $feed, EntityInterface $entity, $target, array $values);

/**
 * Returns if the value for the target is empty.
 *
 * @param \Drupal\feeds\FeedInterface $feed
 *   The feed object.
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The target object.
 * @param string $target
 *   The name of the target to set.
 *
 * @return bool
 *   True if the value on the entity is empty. False otherwise.
 */
public function isEmpty(FeedInterface $feed, EntityInterface $entity, $target);

then it look great)

Thanks for looking, @andypost!

Committed #2.

Automatically closed - issue fixed for 2 weeks with no activity.