simplify fee code

[mvadari]

High Level Overview of Change

Context of Change

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

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.9%. Comparing base (43c80ed) to head (05fab17).

Additional details and impacted files

@@               Coverage Diff                @@
##           ripple/se/fees   #6249     +/-   ##
================================================
- Coverage            79.9%   79.9%   -0.0%     
================================================
  Files                 854     854             
  Lines               73876   73871      -5     
  Branches             8301    8301             
================================================
- Hits                59005   59000      -5     
  Misses              14871   14871             

Files with missing lines	Coverage Δ
src/xrpld/app/misc/FeeVoteImpl.cpp	95.9% <100.0%> (-0.1%)	⬇️

... and 2 files with indirect coverage changes

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