Remove usages of the deprecated std::iterator

[thomasspriggs]

std::iterator is deprecated in C++17, this PR removes our usages of it. This should result in fewer build warnings and support continuing to build cbmc if the class is removed in a future C++ standard.

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• 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).
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[thomasspriggs]

This PR is expected to supersede #7468

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6475b3c) 79.09% compared to head (05020d2) 79.09%.
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8088   +/-   ##
========================================
  Coverage    79.09%   79.09%           
========================================
  Files         1700     1700           
  Lines       196619   196619           
========================================
  Hits        155521   155521           
  Misses       41098    41098           

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