The App has been removed, but user "Copy Space for Confluence" remains as a user in a particular space permission but not as a user in your instance.
When you use Copy Space, the App needs to have permission to complete the actions it is to take, so it is added to the permissions of the space. This is done by Atlassian's Confluence. This is not a "normal" user and is not counted towards your user count.
- To remove them you will just need to remove all permission of the App and Save. Conflunce will then perform the removal. It make some time to update usiually less then 24 hours.
- There is no harm in the user remaining in the permissions
- It is not counted towards your user count
- This does not happen automaticaly upon uninstalling the App due to the API provided by Atlassian.