An unused styling file was removed from the Snailmail Account Follow-up module because it was incorrectly referenced and its rule was not being applied. This is a small cleanup that reduces unnecessary code without changing expected user behavior.

This commit removes the unused `snailmail_account_reports_followup_asset.scss`
file.

Actually, this file was wrongly referenced in the assets bundle since
commit odoo/enterprise@267123d4b758a87607f9023d347c478bbfbcef77 and, thus the single CSS
rule concerned wasn't applied.

Co-authored-by: Romeo Fragomeli <rfr@odoo.com>

This update enriches the Belgian payroll accounting test setup by adding employee skill history information. It helps ensure payroll-related processes are tested with more complete and realistic employee data, reducing the risk of gaps in future changes.