Retire fix1781 amendment

[pratikmankawde]

High Level Overview of Change

This change retires the fix1781 amendment.

Context of Change

Amendments activated for more than 2 years can be retired.
https://xrpl.org/resources/known-amendments#fix1781

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.5%. Comparing base (2bf77cc) to head (8c0c3b9).

Files with missing lines	Patch %	Lines
src/xrpld/app/paths/detail/XRPEndpointStep.cpp	40.0%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #5931     +/-   ##
=========================================
- Coverage     79.5%   78.5%   -0.9%     
=========================================
  Files          817     817             
  Lines        72198   69015   -3183     
  Branches      8293    8267     -26     
=========================================
- Hits         57392   54209   -3183     
  Misses       14806   14806             

Files with missing lines	Coverage Δ
src/xrpld/app/paths/detail/XRPEndpointStep.cpp	83.3% <40.0%> (-0.4%)	⬇️

... and 489 files with indirect coverage changes

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