diff --git a/core/modules/rest/tests/src/Functional/BcTimestampNormalizerUnixTestTrait.php b/core/modules/rest/tests/src/Functional/BcTimestampNormalizerUnixTestTrait.php
deleted file mode 100644
index 054ce7c8aea5a043b07c0641a12229e996bf6df8..0000000000000000000000000000000000000000
--- a/core/modules/rest/tests/src/Functional/BcTimestampNormalizerUnixTestTrait.php
+++ /dev/null
@@ -1,37 +0,0 @@
-<?php
-
-namespace Drupal\Tests\rest\Functional;
-
-@trigger_error(__NAMESPACE__ . '\BcTimestampNormalizerUnixTestTrait is deprecated in Drupal 9.0.0 and will be removed before Drupal 10.0.0. Instead of BcTimestampNormalizerUnixTestTrait::formatExpectedTimestampItemValues(123456789), use (new \DateTime())->setTimestamp(123456789)->setTimezone(new \DateTimeZone("UTC"))->format(\DateTime::RFC3339), see https://www.drupal.org/node/2859657.', E_USER_DEPRECATED);
-
-/**
- * Trait for ResourceTestBase subclasses formatting expected timestamp data.
- */
-trait BcTimestampNormalizerUnixTestTrait {
-
-  /**
-   * Formats a UNIX timestamp.
-   *
-   * @param int $timestamp
-   *   The timestamp value to format.
-   *
-   * @return string
-   *   The formatted RFC3339 date string.
-   *
-   * @see \Drupal\serialization\Normalizer\TimestampItemNormalizer
-   */
-  protected function formatExpectedTimestampItemValues($timestamp) {
-    $date = new \DateTime();
-    $date->setTimestamp($timestamp);
-    // Per \Drupal\Core\TypedData\Plugin\DataType\Timestamp::getDateTime(), they
-    // default to string representations in the UTC timezone.
-    $date->setTimezone(new \DateTimeZone('UTC'));
-
-    // Format is also added to the expected return values.
-    return [
-      'value' => $date->format(\DateTime::RFC3339),
-      'format' => \DateTime::RFC3339,
-    ];
-  }
-
-}