refactor: OPTIC-1678: ff clean up left overs

[luarmr]

Clean up references to:

fflag_fix_back_optic_1526_project_members_prefetch_short;
fflag_fix_front_dev_3617_taxonomy_memory_leaks_fix;
fflag__feature_develop__prompts__dia_1362_custom_llm_endpoint;

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.09%. Comparing base (3900a7a) to head (cc11b39).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7077   +/-   ##
========================================
  Coverage    77.09%   77.09%           
========================================
  Files          183      183           
  Lines        14400    14400           
========================================
  Hits         11101    11101           
  Misses        3299     3299           

Flag	Coverage Δ
pytests	77.09% <ø> (ø)

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