You may have retire your computer from Microsoft Intune Admin Portal. However, the intune client computer still exist.
To do manually, you need to use command line rather than remove from Add/Remove Program.
After execute below command, just wait for a couple minutes. It will disappear from task bar.
|C:\Program Files\Microsoft\OnlineManagement\Common>ProvisioningUtil.exe /UninstallAgents /WindowsIntune|