Remove async-trait crate as dependency for traces

[lalitb]

Changes

traces SDK doesn't have any trait with async fn, so async-trait dependency can be safely removed. We can do similar changes for logs and possibly metrics in 0.28, as it would need exporter interface change.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.5%. Comparing base (e6c351f) to head (6ce5867).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2339     +/-   ##
=======================================
- Coverage   79.5%   79.5%   -0.1%     
=======================================
  Files        123     123             
  Lines      21365   21365             
=======================================
- Hits       17004   17002      -2     
- Misses      4361    4363      +2     

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