[v9] Remove user segment

[buenaflor]

📜 Description

💡 Motivation and Context

Closes #2683

Functionality is not supported anymore

💚 How did you test it?

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.06%. Comparing base (b2409ce) to head (9b12582).
Report is 1 commits behind head on v9.

Additional details and impacted files

@@            Coverage Diff             @@
##               v9    #2687      +/-   ##
==========================================
- Coverage   89.07%   89.06%   -0.01%     
==========================================
  Files         261      261              
  Lines        8860     8847      -13     
==========================================
- Hits         7892     7880      -12     
+ Misses        968      967       -1     

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