remove cloud extension key for vcenter managed vms

When I execute this cmd

Get-VM  |select Name,@{N='Extensionkey';E={$_.ExtensionData.Config.ManagedBy.ExtensionKey}}

Output:

Name         Extensionkey   

----         ------------   

TestVM vCloud Director-1

I got few vms which have extensionkey as vCloud Director-1 but they are no where managed by vcloud so how I can remove that extension key using powercli.