Screenshots need to be updated for new UI

Irfan Sharif (irfansharif) commented:

Re: [Decommission Nodes](https://cockroachlabs.com/docs//v20.1/remove-nodes.html)

Things look a lot different now. 
<img width="1323" alt="image" src="https://user-images.githubusercontent.com/10536690/79514965-62e40280-8015-11ea-9215-0ab90cfd8b00.png">

This may be true for other pages in our UI as well.

Jira Issue: DOC-495