refactor: Remove unused notTooManyOffers function from NFTokenUtils

[Kassaking7]

High Level Overview of Change

Remove unused notTooManyOffers Function from NFTokenUtils file

Context of Change

This function was forgotten to be deleted when we retired some NFT amendments

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)

[yinyiqian1]

LGTM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.5%. Comparing base (b0fe2ec) to head (2df2fc2).
⚠️ Report is 8 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #6737   +/-   ##
=======================================
  Coverage     81.4%   81.5%           
=======================================
  Files         1006    1006           
  Lines        74463   74450   -13     
  Branches      7557    7548    -9     
=======================================
- Hits         60641   60640    -1     
+ Misses       13822   13810   -12     

Files with missing lines	Coverage Δ
include/xrpl/ledger/helpers/NFTokenHelpers.h	100.0% <ø> (ø)
src/libxrpl/ledger/helpers/NFTokenHelpers.cpp	89.7% <ø> (+2.6%)	⬆️

... and 6 files with indirect coverage changes

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[mvadari]

This should be refactor, not chore