[Refactor] Relocate completion and chat completion tests (#37125)

Signed-off-by: sfeng33 <4florafeng@gmail.com>

tests/entrypoints/llm/test_chat.py

@@ -4,12 +4,11 @@ import weakref
 
 import pytest
 
+from tests.entrypoints.openai.chat_completion.test_vision import TEST_IMAGE_ASSETS
 from vllm import LLM
 from vllm.distributed import cleanup_dist_env_and_memory
 from vllm.sampling_params import SamplingParams
 
-from ..openai.test_vision import TEST_IMAGE_ASSETS
-
 
 @pytest.fixture(scope="function")
 def text_llm():