chore: remove unused guzzle6 check (#2694)

Author: bshaffer

src/Http/REST.php

@@ -89,19 +89,6 @@ public static function doExecute(ClientInterface $client, RequestInterface $requ
             }
 
             $response = $e->getResponse();
-            // specific checking for Guzzle 5: convert to PSR7 response
-            if (
-                interface_exists('\GuzzleHttp\Message\ResponseInterface')
-                && $response instanceof \GuzzleHttp\Message\ResponseInterface
-            ) {
-                $response = new Response(
-                    $response->getStatusCode(),
-                    $response->getHeaders() ?: [],
-                    $response->getBody(),
-                    $response->getProtocolVersion(),
-                    $response->getReasonPhrase()
-                );
-            }
         }
 
         return self::decodeHttpResponse($response, $request, $expectedClass);

tests/Google/Http/RESTTest.php

@@ -31,6 +31,7 @@ class RESTTest extends BaseTest
      * @var REST $rest
      */
     private $rest;
+    private Request $request;
 
     public function setUp(): void
     {