Remove Firefox Sync Server (#3179)

Deprecated repository.
Possible replacement https://github.com/mozilla-services/syncstorage-rs not ready for production.
See https://github.com/awesome-selfhosted/awesome-selfhosted/pull/3179

README.md

@@ -247,7 +247,6 @@ Software which allows users to add, annotate, edit, and share [bookmarks](https:
 - [dyu bookmarks](https://github.com/dyu/bookmarks) - Single-threaded/process bookmark app powered by leveldb and uWebSockets. Supports importing from Delicious and Chrome. ([Demo](https://dyuproject.com/bookmarks/)) `Apache-2.0` `Java`
 - [Espial](https://github.com/jonschoning/espial) - An open-source, web-based bookmarking server. `AGPL-3.0` `Haskell`
 - [Firefox Account Server](https://mozilla-services.readthedocs.io/en/latest/howtos/run-fxa.html) - This allows you to host your own Firefox accounts server. ([Source Code](https://github.com/mozilla/fxa)) `MPL-2.0` `Nodejs, Java`
-- [Firefox Sync Server](https://github.com/mozilla-services/syncserver) - Sync Firefox bookmarks, passwords, history, tabs, preferences. `MPL-2.0` `Python`
 - [Geekmarks](https://geekmarks.dmitryfrank.com/) - Personal bookmarking service focused on speed and organization using hierarchical tags. ([Source Code](https://github.com/dimonomid/geekmarks)) `BSD-2-Clause` `Go`
 - [golinks](https://git.mills.io/prologic/golinks) - Web application that allows you to create smart bookmarks, commands and aliases by pointing your web browser's default search engine at a running instance. Similar to bunny1 or yubnub. ([Demo](https://search.mills.io)) `MIT` `Go`
 - [Hackershare](https://github.com/hackershare/hackershare) - Social bookmarks website for hackers. ([Demo](https://hackershare.dev)) `MIT` `Ruby`