Remove Plume. Not actively maintained. (#3427)

According to project website (https://joinplu.me/), this project is no longer actively maintained.  Author directs visitors to other projects.  Last Git commit was 6 months ago.

README.md

@@ -229,7 +229,6 @@ _See also: [WeblogMatrix](https://www.weblogmatrix.org/)_
 - [Haven](https://havenweb.org/) - Private blogging system with markdown editing and built in RSS reader. ([Demo](https://havenweb.org/demo.html), [Source Code](https://github.com/havenweb/haven)) `MIT` `Ruby`
 - [htmly](https://www.htmly.com/) - Databaseless Blogging Platform (Flat-File Blog). ([Demo](https://demo.htmly.com/), [Source Code](https://github.com/danpros/htmly)) `GPL-2.0` `PHP`
 - [Known](https://withknown.com/) - A collaborative social publishing platform. ([Source Code](https://github.com/idno/known)) `Apache-2.0` `PHP`
-- [Plume](https://joinplu.me/) - Federated blogging engine, based on ActivityPub. ([Source Code](https://github.com/Plume-org/Plume)) `AGPL-3.0` `Rust`
 - [PluXml](https://pluxml.org) - XML-based blog/CMS platform. ([Source Code](https://github.com/pluxml/PluXml)) `GPL-1.0` `PHP`
 - [Serendipity](https://docs.s9y.org/) - Serendipity (s9y) is a highly extensible and customizable PHP blog engine using Smarty templating. ([Source Code](https://github.com/s9y/serendipity)) `BSD-3-Clause` `PHP`
 - [WriteFreely](https://writefreely.org) - Writing software for starting a minimalist, federated blog — or an entire community. ([Source Code](https://github.com/writefreely/writefreely)) `AGPL-3.0` `Go`