Refine-arithmetic supports simplifier

[peterschrammel]

This fixes a regression introduced by f1be42c

• Each commit message has a non-empty body, explaining why the change was made.
• [n/a] Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• [n/a] My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• [n/a] White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.37%. Comparing base (0f0aff9) to head (4648353).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8619   +/-   ##
========================================
  Coverage    80.37%   80.37%           
========================================
  Files         1686     1686           
  Lines       206773   206772    -1     
  Branches        85       85           
========================================
+ Hits        166200   166202    +2     
+ Misses       40573    40570    -3     

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[tautschnig]

Thank you!