Remove unused method

[eqbech]

Issue
Resolves #14004

• 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 'just rapid-tests')

When applicable

• When screenshots are changed: Review screenshot-PR in ert-testdata,
  merge screenshot-PR in ert-testdata before merging this PR.
• 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: Add backport label to latest release (format: 'backport release-branch-name')

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.84%. Comparing base (ae2f9f1) to head (8f156d7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14046      +/-   ##
==========================================
- Coverage   91.85%   91.84%   -0.01%     
==========================================
  Files         481      480       -1     
  Lines       33342    33334       -8     
==========================================
- Hits        30626    30616      -10     
- Misses       2716     2718       +2     

Flag	Coverage Δ
cli-tests	36.34% <ø> (+<0.01%)	⬆️
fuzz	44.12% <ø> (-0.02%)	⬇️
gui-tests	58.39% <ø> (-0.05%)	⬇️
performance-and-unit-tests	80.31% <ø> (-0.09%)	⬇️
test	46.47% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ert/gui/ertwidgets/models/selectable_list_model.py	90.32% <ø> (+5.02%)	⬆️

... and 1 file with indirect coverage changes

[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks

---

_{Comparing eqbech:remove-unused-method-from-selectable-list-model (8f156d7) with main (91d37b4)}

[eilskra]

🏎️