Remove namespace_baset::follow(typet)

[kroening]

This method has been deprecated since 19th Feb 2024. There are no uses.

• 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.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• n/a 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 79.46%. Comparing base (ba3b018) to head (9318301).
Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8590      +/-   ##
===========================================
+ Coverage    79.14%   79.46%   +0.32%     
===========================================
  Files         1733     1733              
  Lines       198512   197711     -801     
  Branches     18175    18187      +12     
===========================================
- Hits        157119   157118       -1     
+ Misses       41393    40593     -800     

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