[TEST] Increase seq1/2/3.fa and small.fa sequences and remove unused files in data/

[smehringer]

First commit changes tests because the data changed (Claude corrected the tests).

Next commits delete unused files.

[seqan-actions]

Documentation preview available at https://docs.seqan.de/preview/seqan/chopper/340

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.35%. Comparing base (4d9feff) to head (8b876a3).
⚠️ Report is 133 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #340      +/-   ##
==========================================
- Coverage   95.64%   93.35%   -2.29%     
==========================================
  Files          20       20              
  Lines         758      753       -5     
  Branches       16       18       +2     
==========================================
- Hits          725      703      -22     
- Misses         33       50      +17     

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