Current problem
All emojis in a community are shown to every user.
Proposed change
Add a "Hidden" option to emojis in community settings and a "Use hidden emojis" permission to roles in community settings. This would allow community admins to use emojis in static messages (e.g. a community info channel) that otherwise wouldn't be used in conversation by members. The hidden emojis would still count for the total emoji count.