Remove SIMULATION_JOB keyword

[DanSava]

Issue
Resolves #4955

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'pytest tests/ert/unit_tests -n logical -m "not integration_test"')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.77%. Comparing base (d82fc01) to head (94f1696).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9606      +/-   ##
==========================================
+ Coverage   91.74%   91.77%   +0.02%     
==========================================
  Files         426      426              
  Lines       26559    26551       -8     
==========================================
- Hits        24367    24366       -1     
+ Misses       2192     2185       -7     

Flag	Coverage Δ
cli-tests	39.69% <71.42%> (-0.02%)	⬇️
everest-models-test	34.21% <90.90%> (+0.05%)	⬆️
gui-tests	71.95% <71.42%> (+0.09%)	⬆️
integration-test	38.08% <81.81%> (+0.04%)	⬆️
performance-tests	51.63% <28.57%> (-0.01%)	⬇️
test	39.45% <90.90%> (+0.04%)	⬆️
unit-tests	74.18% <45.45%> (-0.02%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #9606 will not alter performance

_{Comparing remove-simulation-job (94f1696) with main (d82fc01)}

Summary

✅ 24 untouched benchmarks

[verveerpj]

LGTM!

[oyvindeide]

Looks really nice, but would be great with a migration error with a path to resoluation if anyone is using this, it will currently just show up as a warning.

[oyvindeide]

LGTM! Just a minor comment, is it possible to write out an example of how FORWARD_MODEL should be configured with the same args?