Remove CircleCI configuration

.github/CODEOWNERS

 # PATH                                          OWNERS
 /.autogen/                                      @acid-chicken
-/.circleci/                                     @syuilo @acid-chicken
 /.config/                                       @syuilo @AyaMorisawa @mei23 @acid-chicken @rinsuki
 # /.config/mongo_initdb_example.js              @khws4v1
 /.github/                                       @syuilo @AyaMorisawa @acid-chicken

README.md

@@ -4,7 +4,6 @@
 
 <div align="center">
 
-[![CircleCI](https://img.shields.io/circleci/project/github/misskey-dev/misskey.svg?style=for-the-badge&logo=circleci)](https://circleci.com/gh/misskey-dev/misskey)
 [![Dependencies](https://img.shields.io/david/misskey-dev/misskey.svg?style=for-the-badge&logo=npm)](https://david-dm.org/misskey-dev/misskey)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=for-the-badge&logo=github)](http://makeapullrequest.com)
 [![Awesome Humane Tech](https://raw.githubusercontent.com/humanetech-community/awesome-humane-tech/main/humane-tech-badge.svg?sanitize=true)](https://github.com/humanetech-community/awesome-humane-tech)