chore: remove fizz migration files

[zepatrik]

As we'll never use them again at this point, we can clean that up a bit.

[aeneasr]

lgtm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.50%. Comparing base (dc46e8d) to head (9debe50).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4343      +/-   ##
==========================================
- Coverage   78.53%   78.50%   -0.03%     
==========================================
  Files         366      366              
  Lines       27130    27130              
==========================================
- Hits        21306    21299       -7     
- Misses       4200     4205       +5     
- Partials     1624     1626       +2     

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