Allow me to share a few insights about why you can't delete your payroll liabilities.
The accounts used in your payroll liability is a default account. This is the reason why you can't delete your old payroll liabilities.
Here's an article you can read to learn more about your default accounts: How to Manage Default and Special Accounts in the Chart of Accounts?
Fill me in if you have any other questions about your payroll liabilities. I'll be always around to help you.