Hide the disabled 'Add' button in the group folders view

[k-jell]

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Is your feature request related to a problem? Please describe.
When viewing the group folders by clicking on the group folder menu entry in the sidebar, there is a disabled 'Add' button. This has caused some confusion among users of my instance. Maybe it would be a good idea to hide that button since group folders are never created there but in the admin menu.

Describe the solution you'd like
Hide the button so that there is no impression that group folders could be created there if you had the correct permissions.