ci: remove references to CircleCI

It is not used anymore.

README.md

@@ -3,7 +3,6 @@
 > Deltachat-core written in Rust 
 
 [![Rust CI](https://github.com/deltachat/deltachat-core-rust/actions/workflows/ci.yml/badge.svg)](https://github.com/deltachat/deltachat-core-rust/actions/workflows/ci.yml)
-[![CircleCI](https://circleci.com/gh/deltachat/deltachat-core-rust.svg?style=shield)](https://circleci.com/gh/deltachat/deltachat-core-rust/)
 
 ## Installing Rust and Cargo
 

scripts/README.md

@@ -1,16 +1,13 @@
 # Continuous Integration Scripts for Delta Chat
 
 Continuous Integration, run through [GitHub
-Actions](https://docs.github.com/actions),
-[CircleCI](https://app.circleci.com/) and an own build machine.
+Actions](https://docs.github.com/actions)
+and an own build machine.
 
 ## Description of scripts 
 
 - `../.github/workflows` contains jobs run by GitHub Actions.
 
-- `../.circleci/config.yml` describing the build jobs that are run
-  by CircleCI.
-
 - `remote_tests_python.sh` rsyncs to a build machine and runs
   `run-python-test.sh` remotely on the build machine.