SlackUserAdmin::invite not working anymore

[mathieutu]

Hey,

Since it's an undocumented not used by slack method, that needs a legacy token tat we can't create anymore for 3 years, I think we could consider that this method can be deleted.

Or at least we should document that it's not working for new projects. (I've added the package just for that usage, and it doesn't work).

WDYT?

source: https://stackoverflow.com/questions/30955818/slack-api-team-invitation