Remove dysfunctional PREP tests / examples

[sappelhoff]

some tests / examples have not seen a lot of care in the past years. I will try to remove/replace them here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.46%. Comparing base (9667c46) to head (50823e3).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #163      +/-   ##
==========================================
- Coverage   98.60%   98.46%   -0.14%     
==========================================
  Files           7        7              
  Lines         715      715              
==========================================
- Hits          705      704       -1     
- Misses         10       11       +1     

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