To remove unused plug-in from vCenter use Managed Object Reference

Found at http://vcenterservername/mob

Logon with vSphere credentials;

1. Click on content, then
2. Extension manager
3. Find the plug-in which needs to be removed; for example, look for extensionList["VirtualCenter"], the parameter you need is just VirtualCenter
4. Click UnregisterExtension, in the VALUE field, enter the name of the plug-in you wish (in this example it's VirtualCenter
5. Click on Invoke Method (to remove plug-in