I called a web service in SharePoint designer with HTTP delete:
_api/web/lists/getbytitle('title1')/items(1)/roleassignments/getbyprincipalid('1')
The workflow returned "Forbidden" response status and the ULS log :
Exception occured in scope Microsoft.SharePoint.SPRoleAssignment.DeleteObject. Exception=System.Runtime.InteropServices.COMException (0x8102006D): The security validation for this page is invalid. Click Back in your Web browser, refresh the page, and try your operation again.