Remove legacy version check for lightning_utilities >= 0.10

[deependujha]

What does this PR do?

This PR removes the conditional import logic that checked whether lightning_utilities was >= 0.10 before using rank_zero_only. Since requirements.txt now enforces lightning_utilities>=0.10, the version check is no longer necessary.

Changes:

• Removed the version check and fallback import for older versions of lightning_utilities.

• Cleaned up related comments and dead code.

This simplifies the code and avoids maintaining legacy branches that are now unreachable.

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PR review

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📚 Documentation preview 📚: https://pytorch-lightning--20823.org.readthedocs.build/en/20823/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87%. Comparing base (01ba7a1) to head (2d135d4).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #20823   +/-   ##
=======================================
  Coverage      87%      87%           
=======================================
  Files         268      268           
  Lines       23384    23362   -22     
=======================================
- Hits        20330    20325    -5     
+ Misses       3054     3037   -17