Remove Codecov badge

There are now two very different types of coverage (tests and
documentation) and the badge does not appear to have an option for the
flag that can differentiate the two.

README.md

@@ -3,7 +3,6 @@
 # Greenbone Vulnerability Manager
 
 [![GitHub releases](https://img.shields.io/github/release/greenbone/gvmd.svg)](https://github.com/greenbone/gvmd/releases)
-[![Code Documentation Coverage](https://img.shields.io/codecov/c/github/greenbone/gvmd.svg?label=Documentation%20Coverage&logo=codecov)](https://codecov.io/gh/greenbone/gvmd)
 [![Build and Test](https://github.com/greenbone/gvmd/actions/workflows/build-and-test.yml/badge.svg)](https://github.com/greenbone/gvmd/actions/workflows/build-and-test.yml)
 [![Docker Pulls](https://img.shields.io/docker/pulls/greenbone/gvmd.svg)](https://hub.docker.com/r/greenbone/gvmd/)
 [![Docker Image Size](https://img.shields.io/docker/image-size/greenbone/gvmd.svg?maxAge=2592000)](https://hub.docker.com/r/greenbone/gvmd/)