The CloudHealth Agent report under Setup > Data Collection > Agents still shows agents that have been uninstalled.
This is expected behavior. The CloudHealth Agent report under Setup > Data Collection > Agents will always show the last Checkin of the agent including it's last version. When an agent is uninstalled it stops checking in and reporting data to the CloudHealth platform. This can be seen by the following (show Late Checkin icon, Last Agent Upload date, Last Agent Checkin date).