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 78.20%. Comparing base (6eedfbe) to head (93eb4f6).

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    78.31%   78.20%   -0.12%     
===========================================
  Files           76       76              
  Lines         7591     7523      -68     
  Branches      1120     1111       -9     
===========================================
- Hits          5945     5883      -62     
+ Misses        1460     1457       -3     
+ Partials       186      183       -3     

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