remove synctube demo link (error 503)

- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2266

README.md

@@ -1263,7 +1263,7 @@ _See also: [List of streaming media systems - Wikipedia](https://en.wikipedia.or
 - [ShinobiCE](https://gitlab.com/Shinobi-Systems/ShinobiCE) - Open Source CCTV software written in Node with both IP and local camera support. `AGPL-3.0/GPL-3.0` `Nodejs`
 - [SRS](https://ossrs.io/) - A simple, high efficiency and real-time video server, supports RTMP, WebRTC, HLS, HTTP-FLV and SRT. ([Source Code](https://github.com/ossrs/srs)) `MIT` `Docker/C++`
 - [Streama](https://github.com/streamaserver/streama) - Self hosted streaming media server. `MIT` `Java`
-- [SyncTube](https://github.com/RblSb/SyncTube) - Lightweight and very simple to setup CyTube alternative to watch videos with friends and chat. ([Demo](https://synctube-example.herokuapp.com/)) `MIT` `Nodejs/Haxe`
+- [SyncTube](https://github.com/RblSb/SyncTube) - Lightweight and very simple to setup CyTube alternative to watch videos with friends and chat. `MIT` `Nodejs/Haxe`
 - [Tube](https://git.mills.io/prologic/tube) - Youtube-like (_without censorship and features you don't need!_) Video Sharing App written in Go which also supports automatic transcoding to MP4 H.265 AAC, multiple collections and RSS feed. ([Demo](https://tube.mills.io)) `MIT` `Go`
 - [VideoLAN Client (VLC)](https://www.videolan.org/) - Cross-platform multimedia player client and server supporting most multimedia files as well as DVDs, Audio CDs, VCDs, and various streaming protocols. ([Source Code](https://github.com/videolan/vlc)) `GPL-2.0` `C`
 - [Zoneminder](https://www.zoneminder.com/) - Closed-circuit television (CCTV) software application which supports IP, USB and Analog cameras. ([Source Code](https://github.com/ZoneMinder/ZoneMinder)) `GPL-2.0` `PHP`