Remove wiki (unmaintained since 2021) (#4065)

- https://git.mills.io/prologic/wiki/commits/branch/master
- ref. #3558

README.md

@@ -2108,7 +2108,6 @@ _See also: [Wikimatrix](https://www.wikimatrix.org/), [List of wiki software - W
 - [TWiki](https://twiki.org/) - TWiki is a Perl-based structured wiki application, typically used to run a collaboration platform, knowledge or document management system, a knowledge base, or team portal. ([Demo](https://twiki.org/cgi-bin/view/Sandbox/WebHome), [Source Code](http://svn.twiki.org/svn/twiki/)) `GPL-2.0` `Perl`
 - [WackoWiki](https://wackowiki.org/) - WackoWiki is a light and easy to install multilingual Wiki-engine. ([Source Code](https://github.com/WackoWiki/wackowiki)) `BSD-3-Clause` `PHP`
 - [Wiki.js](https://js.wiki/) - Modern, lightweight and powerful wiki app using Git and Markdown. ([Demo](https://docs.requarks.io), [Source Code](https://github.com/Requarks/wiki)) `AGPL-3.0` `Nodejs`
-- [wiki](https://git.mills.io/prologic/wiki) - Simple Markdown based wiki engine. ([Demo](https://wiki.mills.io)) `MIT` `Go`
 - [WiKiss](https://wikiss.tuxfamily.org/) - Wiki, simple to use and install. ([Source Code](https://svnweb.tuxfamily.org/listing.php?repname=wikiss/svn&path=%2F&sc=0)) `GPL-2.0` `PHP`
 - [Wikmd](https://github.com/Linbreux/wikmd) - Modern and simple file based wiki that uses Markdown and Git. `MIT` `Python`
 - [XWiki](https://www.xwiki.org) - Second generation wiki that allows the user to extend its functionalities with a powerful extension-based architecture. ([Demo](https://playground.xwiki.org), [Source Code](https://github.com/xwiki/xwiki-platform)) `LGPL-2.1` `Java`