Supress "to subscribe" link on group page if empty

[cindymorgan]

Description

https://datatracker.ietf.org/group/rsab/about/ currently shows a "To subscribe" field with nothing in it. It would be nice to have that field not show up, since subscription to the list is closed. (The list address itself and archive link should both show up, since both are public.)

Code of Conduct

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