[Feature] Deprecate etf.holdings_performance endpoint

[hjoaquim]

1. Why? (1-3 sentences or a bullet point list):

   • Remove deprecated endpoint.

2. What? (1-3 sentences or a bullet point list):

   • Remove code and tests refering to such endpoint.

3. Impact (1-2 sentences or a bullet point list):

   • Minimal

Impact analysis

  User Experience (UX) Impact:
    3: Noticeable UI/UX changes, some user guidance needed
    
> Endpoint is gone.

Performance Impact:
    0: Neutral

Compatibility Impact:
    3: Moderate adaptation for compatibility
    
    > Endpoint not supported in future versions.

Security Impact:
    0: Neutral

Scalability Impact:
    0: Neutral

Maintenance Impact:
    0: Reduces maintenance

Compliance Impact:
    0: Fully compliant, no changes

Dependency Impact:
    0: No change

Scoring:
Total Score: 6 / 40

4. Testing Done:

   • Run unit and integration tests (etf only).