refactor(a2a): drop dead openai_chunk_to_a2a_chunk helper

The deprecated single-chunk helper has no callers anywhere in the
codebase — the streaming path emits proper A2A events via
create_task_event / create_status_update_event /
create_artifact_update_event in handler.py. Removing the dead method
also eliminates the inconsistency where the unused chunk inlined the
envelope-level final flag inside the Message result.

litellm/a2a_protocol/litellm_completion_bridge/transformation.py

@@ -304,55 +304,3 @@ class A2ACompletionBridgeTransformation:
             },
         }
 
-    @staticmethod
-    def openai_chunk_to_a2a_chunk(
-        chunk: Any,
-        request_id: Optional[str] = None,
-        is_final: bool = False,
-    ) -> Optional[Dict[str, Any]]:
-        """
-        Transform a LiteLLM streaming chunk to A2A streaming format.
-
-        NOTE: This method is deprecated for streaming. Use the event-based
-        methods (create_task_event, create_status_update_event,
-        create_artifact_update_event) instead for proper A2A streaming.
-
-        Args:
-            chunk: LiteLLM ModelResponse chunk
-            request_id: Original A2A request ID
-            is_final: Whether this is the final chunk
-
-        Returns:
-            A2A streaming chunk dict or None if no content
-        """
-        # Extract delta content
-        content = ""
-        if chunk is not None and hasattr(chunk, "choices") and chunk.choices:
-            choice = chunk.choices[0]
-            if hasattr(choice, "delta") and choice.delta:
-                content = choice.delta.content or ""
-
-        if not content and not is_final:
-            return None
-
-        # Build A2A streaming chunk. Mirrors the non-streaming response
-        # shape (``result`` is the message itself, with ``kind: "message"``
-        # as the result-level event discriminator — matching how
-        # ``create_artifact_update_event`` uses ``kind: "artifact-update"``
-        # at the result level). ``final`` is an envelope-level streaming
-        # property per the A2A spec and is appended alongside the message
-        # fields so consumers can read a uniform ``result`` shape across
-        # streaming and non-streaming.
-        a2a_chunk = {
-            "jsonrpc": "2.0",
-            "id": request_id,
-            "result": {
-                "kind": "message",
-                "role": "agent",
-                "parts": [{"kind": "text", "text": content}],
-                "messageId": uuid4().hex,
-                "final": is_final,
-            },
-        }
-
-        return a2a_chunk