Removing Actor.im as it's no longer maintained (#1383)

README.md

@@ -241,7 +241,6 @@ _CalDAV or CardDAV clients._
 
 ### Custom communication systems
 
-- [Actor](https://actor.im/) - Actor is a fast, open source messaging platform with rich mobile and web clients. ([Demo](https://app.actor.im), [Source Code](https://github.com/actorapp/actor-platform)) `AGPL-3.0` `Scala`
 - [Broid](https://broid.ai) - Broid enables rich conversations on all messaging channels within a single schema integration using W3C standards. ([Demo](https://www.broid.ai), [Source Code](https://github.com/broidHQ/integrations)) `AGPL-3.0` `Nodejs`
 - [Centrifugo](https://github.com/centrifugal/centrifugo) - Language-agnostic real-time messaging (Websocket or SockJS) server. ([Demo](https://github.com/centrifugal/centrifugo#demo)) `MIT` `Go`
 - [Cherry](https://github.com/rafael-santiago/cherry) - Tiny webchat server. `GPL-2.0` `Go`