style(guardrails): drop the explanatory comment on the choice index field

AGENTS.md keeps explanatory comments out of the code, and the field's own docstring already says what it is for.

litellm/integrations/custom_guardrail.py

@@ -1414,8 +1414,6 @@ class CustomGuardrail(CustomLogger):
             end_time=end_time,
             duration=duration,
             masked_entity_count=masked_entity_count,
-            # Set by callers that inspect one choice at a time, so the per-choice entries of an
-            # n > 1 response can be told apart.
             choice_index=request_data.get("guardrail_choice_index"),
             **(tracing_detail or {}),
         )