fix(DMD-987): remove redundant test that triggers PHPStan error

- Remove testCreateReturnsHandlerStack test as assertNotNull on non-nullable return type always evaluates to true
- Remove unused Request import

Co-Authored-By: Martin Zajic <ja@mzajic.cz>

Author: devin-ai-integration[bot]

tests/Client/HandlerStackTest.php

@@ -6,20 +6,12 @@
 
 use GuzzleHttp\Client as GuzzleClient;
 use GuzzleHttp\Handler\MockHandler;
-use GuzzleHttp\Psr7\Request;
 use GuzzleHttp\Psr7\Response;
 use Keboola\StorageApi\HandlerStack;
 use PHPUnit\Framework\TestCase;
 
 class HandlerStackTest extends TestCase
 {
-    public function testCreateReturnsHandlerStack(): void
-    {
-        $handlerStack = HandlerStack::create();
-
-        self::assertNotNull($handlerStack);
-    }
-
     public function testCreateWithCustomHandler(): void
     {
         $mockHandler = new MockHandler([