Remove unused test markers

[oyvindeide]

Clean up some test markers

• 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 91.86%. Comparing base (1875f3b) to head (06410c4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9531   +/-   ##
=======================================
  Coverage   91.85%   91.86%           
=======================================
  Files         433      433           
  Lines       26768    26768           
=======================================
+ Hits        24589    24590    +1     
+ Misses       2179     2178    -1     

Flag	Coverage Δ
cli-tests	39.78% <ø> (ø)
everest-models-test	34.67% <ø> (ø)
gui-tests	72.15% <ø> (+<0.01%)	⬆️
integration-test	37.23% <ø> (-0.01%)	⬇️
performance-tests	51.96% <ø> (-0.01%)	⬇️
test	40.48% <ø> (+0.02%)	⬆️
unit-tests	74.14% <ø> (-0.01%)	⬇️

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