Remove legacy code

[tristanlatr]

fix #852

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.79%. Comparing base (aedb970) to head (bb3233d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #853      +/-   ##
==========================================
+ Coverage   92.63%   92.79%   +0.15%     
==========================================
  Files          47       47              
  Lines        8489     8468      -21     
  Branches     1557     1550       -7     
==========================================
- Hits         7864     7858       -6     
+ Misses        358      350       -8     
+ Partials      267      260       -7     

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[github-actions]

According to pydoctor_primer, this change doesn't affect pydoctor warnings on a corpus of open source code. ✅