remove 'entity_resolver'

Closes #2930243

core/modules/serialization/src/EntityResolver/ChainEntityResolver.php

-<?php
-
-namespace Drupal\serialization\EntityResolver;
-
-use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
-
-/**
- * Resolver delegating the entity resolution to a chain of resolvers.
- */
-class ChainEntityResolver implements ChainEntityResolverInterface {
-
-  /**
-   * The concrete resolvers.
-   *
-   * @var \Drupal\serialization\EntityResolver\EntityResolverInterface[]
-   */
-  protected $resolvers = [];
-
-  /**
-   * Constructs a ChainEntityResolver object.
-   *
-   * @param \Drupal\serialization\EntityResolver\EntityResolverInterface[] $resolvers
-   *   The array of concrete resolvers.
-   */
-  public function __construct(array $resolvers = []) {
-    $this->resolvers = $resolvers;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function addResolver(EntityResolverInterface $resolver) {
-    $this->resolvers[] = $resolver;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function resolve(NormalizerInterface $normalizer, $data, $entity_type) {
-    foreach ($this->resolvers as $resolver) {
-      $resolved = $resolver->resolve($normalizer, $data, $entity_type);
-      if (isset($resolved)) {
-        return $resolved;
-      }
-    }
-  }
-
-}