if you have physical possession of the device
and you erase all content and settings on the actual device, this removes it from iCloud. and that is all you need to do
if you go to iCloud.com and erase your iPad, this will keep your iPad on your iCloud account, and then
you must remove it from iCloud using the website, or it will never allow itself to be activated.
i did that once when i sold my iPad on eBay.
i erased my iPad using iCloud
and shipped it, and once the guy signed for it and said he got it okay, i removed it from iCloud
and all he had to do was set it up and it worked
the screen said it was locked ! but when he clicked start over and tried connected it to wifi
the warning jut disappeared and it was like setting up a new iPad