test(test_completion.py): fix test

litellm/tests/test_completion.py

@@ -97,8 +97,6 @@ def test_null_role_response():
     """
     import openai
 
-    litellm.success_callback = ["lunary"]
-
     openai_client = openai.OpenAI()
     with patch.object(
         openai_client.chat.completions, "create", side_effect=_openai_mock_response
@@ -114,8 +112,6 @@ def test_null_role_response():
 
         assert response.choices[0].message.role == "assistant"
 
-    assert False
-
 
 def test_completion_azure_command_r():
     try: