Remove cli.py

[hannahbaumann]

As discussed, this PR removes the cli.py as we decided that this package will not have a CLI, but that important commands may live in the openfe package.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.19%. Comparing base (5260e3b) to head (09e988a).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #86      +/-   ##
==========================================
+ Coverage   88.16%   89.19%   +1.03%     
==========================================
  Files           7        6       -1     
  Lines         338      324      -14     
==========================================
- Hits          298      289       -9     
+ Misses         40       35       -5     

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