gh actions: drop codecov

This now fails with

```
{'detail': ErrorDetail(string='Unable to locate build via Github Actions API. Please upload with the Codecov repository upload token to resolve issue.', code='not_found')}
```

.github/workflows/build.yml

@@ -44,18 +44,6 @@ jobs:
         run: |
           source ./env/bin/activate
           python setup.py install
-      - name: Generate coverage report
-        run: |
-          source ./env/bin/activate
-          pip install pytest-cov
-          pytest --cov=./ --cov-report=xml
-      - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v1
-        with:
-          file: ./coverage.xml
-          flags: unittests
-          name: codecov-umbrella
-          fail_ci_if_error: true
       - name: Docs
         run: |
           source ./env/bin/activate

README.rst

@@ -2,7 +2,7 @@
 afew
 ====
 
-|GithubTag| |CodeCov| |CI Status|
+|GithubTag| |CI Status|
 
 About
 -----
@@ -68,7 +68,5 @@ Have fun :)
 
 .. |GithubTag| image:: https://img.shields.io/github/tag/afewmail/afew.svg
     :target: https://github.com/afewmail/afew/releases
-.. |CodeCov| image:: https://codecov.io/gh/afewmail/afew/branch/master/graph/badge.svg
-    :target: https://codecov.io/gh/afewmail/afew
 .. |CI Status| image:: https://github.com/afewmail/afew/workflows/CI/badge.svg
     :target: https://github.com/afewmail/afew/actions