This reverts commit 7d8ae1a.

…tale results.json (#2631)

The endpoints accuracy artifact was renamed from results.json (with a
responses field) to accuracy/accuracy_results.json in
mlcommons/endpoints#400, which also dropped the responses field
entirely (per-sample text now lives in events.jsonl, not part of the
submission). truncate_accuracy_log.py still looked for the old
results.json/responses shape and would only log "missing" for every
endpoints submission. Detect the endpoints layout via the scenario-root
config.yaml and skip truncation, and remove the now-dead
PERFORMANCE_ENDPOINTS_DIR/ACCURACY_ENDPOINTS_DIR constants left over
from the loader.py refactor to ENDPOINTS_SCENARIO_DIR.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>