fix: remove unused variable original_guardrails in pipeline_executor

Remove unused local variable 'original_guardrails' that was assigned
but never used in the _execute_guardrail_step method.

Fixes Ruff F841 linting error.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

litellm/proxy/policy_engine/pipeline_executor.py

@@ -154,7 +154,6 @@ class PipelineExecutor:
             # Inject guardrail name into metadata so should_run_guardrail() allows it
             if "metadata" not in data:
                 data["metadata"] = {}
-            original_guardrails = data["metadata"].get("guardrails")
             data["metadata"]["guardrails"] = [step.guardrail]
 
             # Use unified_guardrail path if callback implements apply_guardrail