Deleted Computers get the "Delete" option when selected in the "Deleted Objects" container. When you delete the object, it shows successfull, but the computer object is never gone from the "Deleted objects" container:

Note that if you run the following native Powerhsell cmdlet, the object it is gone from the "Deleted Objects" container:
Get-ADObject -Filter 'isDeleted -eq $true -and Name -like "ComputerName*"' -IncludeDeletedObjects | Remove-ADObject -Confirm:$false