Merge bitcoin-core/secp256k1#1430: README: remove CI badge

5dab0ba README: remove CI badge (Jonas Nick)

Pull request description:

ACKs for top commit:
  sipa:
    utACK 5dab0ba
  real-or-random:
    utACK 5dab0ba

Tree-SHA512: 56730fa8067cc48b8e5af6fc21b0cd6c47f615c5ebba9edcf29ca5eaf7b2359662a9af219612e80688d8f8939649c7c3c26136c0442ba47d56251a0d92cf984a

README.md

@@ -1,7 +1,6 @@
 libsecp256k1
 ============
 
-[![Build Status](https://api.cirrus-ci.com/github/bitcoin-core/secp256k1.svg?branch=master)](https://cirrus-ci.com/github/bitcoin-core/secp256k1)
 ![Dependencies: None](https://img.shields.io/badge/dependencies-none-success)
 [![irc.libera.chat #secp256k1](https://img.shields.io/badge/irc.libera.chat-%23secp256k1-success)](https://web.libera.chat/#secp256k1)