SideCondition.toRepresentation: remove mapVariables

[ana-pantilie]

Fixes #2476
Fixes #2485

There is a space leak related to TermLike.traverseVariables, and c35bfa5 increased the size of the SideCondition and therefore the number of times this function is called.

We discussed that the mapVariables call here is not entirely correct (because it erases the RewritingVariable information) and that it's actually no longer necessary since the simplifier only uses one variable type now anyway.

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Review checklist

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• Summary. Write a summary of the changes. Explain what you did to fix the issue, and why you did it. Present the changes in a logical order. Instead of writing a summary in the pull request, you may push a clean Git history.
• Documentation. Write documentation for new functions. Update documentation for functions that changed, or complete documentation where it is missing.
• Tests. Write unit tests for every change. Write the unit tests that were missing before the changes. Include any examples from the reported issue as integration tests.
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[virgil-serbanuta]

Thanks!