Remove ErtConfig from EverestRunModel

[frode-aarstad]

Issue
Resolves #9789

Approach
Short description of the approach

(Screenshot of new behavior in GUI if applicable)

• 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 tests/everest -n auto --hypothesis-profile=fast -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

[codspeed-hq]

CodSpeed Performance Report

Merging #9869 will improve performances by 10.33%

_{Comparing frode-aarstad:remove-ert-config (347507a) with main (cb0726d)}

Summary

⚡ 1 improvements
✅ 24 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	test_load_from_context[gen_x: 20, sum_x: 20 reals: 10]	7 ms	6.3 ms	+10.33%

[yngve-sk]

I think the code corresponding to this in everest_to_ert.py can be removed now that this is done here, as well as the test test_everest_to_ert_controls