docs: Remove buildkite badge from README

Author: fmoko

README.md

@@ -3,7 +3,7 @@
 [![All Contributors](https://img.shields.io/badge/all_contributors-68-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
-# rustlings 🦀❤️ [![Build status](https://badge.buildkite.com/7af93d81dc522c67a1ec8e33ff5705861b1cb36360b774807f.svg)](https://buildkite.com/mokou/rustlings)
+# rustlings 🦀❤️
 
 Greetings and welcome to `rustlings`. This project contains small exercises to get you used to reading and writing Rust code. This includes reading and responding to compiler messages!