We had Nintex installed in our 2013 Standard farm. After uninstall, I am getting errors on event logs

EVENT ID 6644

Source: SharePoint Foundation (Microsoft-SharePoint Products-SharePoint Foundation)

Event manager error: Could not load file or assembly 'Nintex.Workflow, Version=1.0.0.0, Culture=neutral, PublicKeyToken=913f6bae0ca5ae12' or one of its dependencies. The system cannot find the file specified.

How to clean?