Dead Code: Remove unused compute_health_score function from metrics_extractor.py

[eshaanag]

What is missing / Why it matters

The metrics_extractor.py file contains a duplicate compute_health_score function at the bottom. Since health scoring logic was fully moved and refactored into health_scorer.py, this older implementation is dead code and is never imported or called anywhere in the backend. Removing it cleans up the codebase and prevents confusion for new contributors.

Acceptance Criteria

• Delete compute_health_score from backend/features/repo_ingestion/metrics_extractor.py.
• Verify that pytest tests pass successfully.
• Ensure no other files reference this function.