Remove comment section when feature is closed or completed

When a feature is set to complete to closed, the user is still presented with the text "No comments yet. Be the first to start the discussion". This can be very confusing, because there's no way to start a discussion. For example this thread: https://demo.sleekplan.app/feedback/7402 It would be better to have a different message such as "this thread is closed/completed" to avoid confusion.