remove Abilian SBE (unmaintained) (#3517)

- unmaintained since 2021
- requires EOL python 2.7
- no activity in issue tracker
- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2266

README.md

@@ -513,7 +513,6 @@ Simple deployment of [E-mail](https://en.wikipedia.org/wiki/Email) servers, e.g.
 
 [Social Networking](https://en.wikipedia.org/wiki/Social_networking_service) and [Forum](https://en.wikipedia.org/wiki/Internet_forum) software.
 
-- [Abilian SBE](https://github.com/abilian/abilian-sbe) - Open Source Collaboration and Social Networking framework and platform. `LGPL-2.1` `Python`
 - [Akkoma](https://akkoma.social/) - Federated microblogging server with Mastodon, GNU social, and ActivityPub compatibility. ([Source Code](https://akkoma.dev/AkkomaGang/akkoma)) `AGPL-3.0` `Elixir`
 - [Anahita](https://www.getanahita.com/) - Open Source Social Networking Framework and Platform. ([Source Code](https://github.com/anahitasocial/anahita)) `GPL-3.0` `PHP`
 - [AsmBB](https://board.asm32.info) - A fast, SQLite-powered forum engine written in ASM. ([Source Code](https://asm32.info/fossil/asmbb/index)) `EUPL-1.2` `Assembly`