refactor: OPTIC-925: Remove Stale Feature Flag - fix_back_dev_3351_ml_validation_error_extension_short

[luarmr]

…_validation_error_extension_short

PR fulfills these requirements

• Commit message(s) and PR title follows the format [fix|feat|ci|chore|doc]: TICKET-ID: Short description of change made ex. fix: DEV-XXXX: Removed inconsistent code usage causing intermittent errors
• Tests for the changes have been added/updated (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)
• Best efforts were made to ensure docs/code are concise and coherent (checked for spelling/grammatical errors, commented out code, debug logs etc.)
• Self-reviewed and ran all changes on a local instance (for bug fixes/features)

Change has impacts in these area(s)

(check all that apply)

• Product design
• Backend (Database)
• Backend (API)
• Frontend

Describe the reason for change

Remove long time stale feature flag
I need to wait for selenium here and other test, since LD show enabled for tests

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.70%. Comparing base (e6e68f0) to head (1907d71).
Report is 13 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6647      +/-   ##
===========================================
+ Coverage    76.67%   76.70%   +0.02%     
===========================================
  Files          169      169              
  Lines        13844    13848       +4     
===========================================
+ Hits         10615    10622       +7     
+ Misses        3229     3226       -3     

Flag	Coverage Δ
pytests	76.70% <100.00%> (+0.02%)	⬆️

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