Maintenance: Remove outdated and obsolete coveralls badge.

README.md

@@ -13,7 +13,7 @@ You're going to love Zammad!
 
 - CI: ![ci](https://github.com/zammad/zammad/workflows/ci/badge.svg)
 - Build Docker images: ![build-docker-compose-images](https://github.com/zammad/zammad/workflows/build-docker-compose-images/badge.svg) ![build-docker-image](https://github.com/zammad/zammad/workflows/build-docker-image/badge.svg)
-- Code: [![Code Climate](https://codeclimate.com/github/zammad/zammad/badges/gpa.svg)](https://codeclimate.com/github/zammad/zammad) [![Coverage Status](https://coveralls.io/repos/github/zammad/zammad/badge.svg)](https://coveralls.io/github/zammad/zammad)
+- Code: [![Code Climate](https://codeclimate.com/github/zammad/zammad/badges/gpa.svg)](https://codeclimate.com/github/zammad/zammad)
 - Docs: [![Documentation Status](https://readthedocs.org/projects/zammad/badge/)](https://docs.zammad.org)
 - Issues: [![Percentage of issues still open](http://isitmaintained.com/badge/open/zammad/zammad.svg)](https://github.com/zammad/zammad/issues "Percentage of issues still open") [![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/zammad/zammad.svg)](https://github.com/zammad/zammad/issues?q=is%3Aissue+is%3Aclosed "Average time to resolve an issue")
 - Download DEB/RPM: [![](https://img.shields.io/badge/Branch-develop-lightgrey.svg)](https://packager.io/gh/zammad/zammad#develop) [![](https://img.shields.io/badge/Branch-stable-lightgrey.svg)](https://packager.io/gh/zammad/zammad#stable)