remove PushJet (unmaintained)

https://github.com/Pushjet/Pushjet-Server-Api/issues/35
Fixes https://github.com/Kickball/awesome-selfhosted/issues/1648

README.md

@@ -282,7 +282,6 @@ _CalDAV or CardDAV clients._
 - [Mibew](https://mibew.org) - Mibew Messenger is an open-source live support application written in PHP and MySQL. It enables one-on-one chat assistance in real-time directly from your website. ([Demo](https://mibew.org/demo2), [Source Code](https://github.com/Mibew/mibew)) `Apache-2.0` `PHP`
 - [Mumble](http://wiki.mumble.info/wiki/Main_Page) - Low-latency, high quality voice/text chat software. ([Source Code](https://github.com/mumble-voip/mumble), [Clients](https://wiki.mumble.info/wiki/3rd_Party_Applications)) `BSD-3-Clause` `C++`
 - [Node-Chat](https://github.com/IgorAntun/node-chat) - Not-so-basic open-source chat with admin features. `MIT` `Nodejs`
-- [Pushjet](https://pushjet.io/) - Self hosted push notification service built with a simple API making sending notifications easy. ([Source Code](https://github.com/Pushjet/Pushjet-Server-Api)) `BSD-2-Clause` `Python`
 - [Rallly](http://rallly.co) - Rallly is a free collaborative scheduling service. ([Source Code](https://github.com/lukevella/Rallly)) `CC-BY-SA-4.0` `Nodejs`
 - [RetroShare](http://retroshare.org) - Secured and decentralized communication system. Offers decentralized chat, forums, messaging, file transfer. ([Source Code](https://github.com/RetroShare/RetroShare)) `GPL-2.0` `С++`
 - [Jami](https://jami.net/) - Free and universal communication platform which preserves the user's privacy and freedoms (formerly GNU Ring). ([Source Code](https://git.ring.cx/savoirfairelinux/ring-project)) `GPL-3.0` `C++`