refactor: remove spurious addition

Author: omgitsaheadcrab

instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py

@@ -845,7 +845,6 @@ async def otel_send(message: dict[str, Any]):
             status_code = None
             if message["type"] == "http.response.start":
                 status_code = message["status"]
-                expecting_trailers = message.get("trailers", False)
             elif message["type"] == "websocket.send":
                 status_code = 200