fix(OpenAI): Remove assistants beta header (#175)

Author: edvardsr

src/ServiceProvider.php

@@ -35,7 +35,6 @@ public function register(): void
             $client = OpenAI::factory()
                 ->withApiKey($apiKey)
                 ->withOrganization($organization)
-                ->withHttpHeader('OpenAI-Beta', 'assistants=v2')
                 ->withHttpClient(new \GuzzleHttp\Client(['timeout' => config('openai.request_timeout', 30)]));
 
             if (is_string($project)) {