[Hotfix Main]: [docs] Delete wall formulations from docstring

[github-actions]

Hotfix of PR #1932 (#1932) to the main branch.
Hey @piotrkluba, please review this hotfix PR created from your original PR.

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Note

Low Risk
Low risk documentation-only change with no impact on runtime behavior or APIs.

Overview
Removes the wall_formulations reference line from the Wall boundary condition docstring in surface_models.py, leaving the rest of the examples and model behavior unchanged.

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