Remove product filters require

[forkata]

Summary

This change removes the explicit require for product filters to simplify overriding it in client applications. We have confirmed that only the test files that require the filters depend on them. The product filters are also explicitly required in the solidus_starter_frontend which depends on them.

Fixes #6406

Checklist

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[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.49%. Comparing base (714b3ec) to head (d7cb914).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
core/lib/spree/core/product_filters.rb	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6408      +/-   ##
==========================================
- Coverage   89.50%   89.49%   -0.01%     
==========================================
  Files         981      981              
  Lines       20479    20476       -3     
==========================================
- Hits        18329    18326       -3     
  Misses       2150     2150              

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[forkata]

I don't believe the code coverage changed here, I think the check here is just indicating that the product filters specs did not cover all the code paths. We can look at adding some code coverage if that's needed to merge this change.

[kennyadsl]

👍 I don't think it's needed to add more coverage for the purpose of this PR. Thanks!