Issue #3279103 by bradjones1: Test cleanup: Remove dead code from JsonApiFunctionalTest

(cherry picked from commit bf7ce2f8)

core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php

@@ -639,7 +639,6 @@ public function testWrite() {
       'auth' => [$this->user->getAccountName(), $this->user->pass_raw],
       'headers' => ['Accept' => 'application/vnd.api+json'],
     ]);
-    $created_response = Json::decode($response->getBody()->__toString());
     $this->assertEquals(415, $response->getStatusCode());
 
     // 4. Article with a duplicate ID.
@@ -666,7 +665,6 @@ public function testWrite() {
       'auth' => [$this->user->getAccountName(), $this->user->pass_raw],
       'headers' => ['Content-Type' => 'application/vnd.api+json'],
     ]);
-    $created_response = Json::decode($response->getBody()->__toString());
     $this->assertEquals(404, $response->getStatusCode());
     // 6. Decoding error.
     $response = $this->request('POST', $collection_url, [