No such endpoint is currently documented for Helix: https://dev.twitch.tv/docs/api/reference.
Twitch API v5 is deprecated and will be removed on 12/31/18. The new Twitch API is live and we are actively adding new functionality to it. (source)
Expect that Helix will receive an endpoint to replace getUsers, but for now it is still appropriate to use Kraken.
edit: see post below