Cleanup tests to deduplicate static response construction

Author: tconley1428

temporalio/contrib/openai_agents/_temporal_openai_agents.py

@@ -79,8 +79,6 @@ def set_open_ai_agent_temporal_overrides(
         A context manager that yields the configured TemporalTraceProvider.
 
     """
-    if model_params is None:
-        model_params = ModelActivityParameters()
 
     previous_runner = get_default_agent_runner()
     previous_trace_provider = get_trace_provider()