Refactor / remove ensemble.from_yaml/toml/json

[jlnav]

I think I was the only one who ever used these features... so lets clean these up.

Edit, December thoughts: being able to generate scripts via AI, plus our upcoming development with using VOCS to populate sim/gen specs, plus other interface changes, means that I'd have to update these features for that; and there's not much evidence there's a demand.

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.41%. Comparing base (229f7f9) to head (0d03ef1).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
libensemble/ensemble.py	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1605      +/-   ##
===========================================
+ Coverage    93.33%   93.41%   +0.07%     
===========================================
  Files           76       76              
  Lines         7580     7512      -68     
  Branches      1119     1110       -9     
===========================================
- Hits          7075     7017      -58     
+ Misses         330      325       -5     
+ Partials       175      170       -5     

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