Remove 'new parent hash' assert

[Bronek]

This assert is known to occasionally trigger, without causing errors downstream. Replace it with a log message.

High Level Overview of Change

Remove assert which is known to occasionally fail, without causing any problems.

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)

[ximinez]

Thank you for taking care of this nagging issue.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.2%. Comparing base (ab44cc3) to head (0841d7f).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/xrpld/app/misc/detail/TxQ.cpp	75.0%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #5313     +/-   ##
=========================================
- Coverage     78.2%   78.2%   -0.0%     
=========================================
  Files          790     790             
  Lines        67738   67739      +1     
  Branches      8177    8178      +1     
=========================================
- Hits         52962   52954      -8     
- Misses       14776   14785      +9     

Files with missing lines	Coverage Δ
src/xrpld/app/misc/TxQ.h	98.2% <ø> (ø)
src/xrpld/app/misc/detail/TxQ.cpp	98.6% <75.0%> (-0.1%)	⬇️

... and 5 files with indirect coverage changes

[intelliot]

Out of curiosity, in what situations would this assert trigger?

When the parent ledger hash is unchanged, then the ledger has not advanced, right? Why would the same ledger be processed again?

If it is expected behavior (when?) then we could consider having the log at info. But if it does indicate something problematic, then warn is appropriate.