Drop CodeCov from CI (wasn't working) (#4723)

Currently this sometimes causes a CI failure, and isn't doing anything useful due to changes on the CodeCov side.

Closes #3752.

.appveyor.yml

@@ -46,7 +46,3 @@ test_script:
   - coverage run run_tests.py --offline
   - coverage xml
   - cd ..
-
-after_test:
-  - conda install -c conda-forge codecov
-  - codecov --file Tests/coverage.xml -X pycov -X gcov

.github/workflows/ci.yml

@@ -201,12 +201,10 @@ jobs:
       run: |
         python -m pip install .
 
-    - name: Run test suite and get coverage
+    - name: Run test suite
       run: |
         cd Tests
-        rm -rf coverage.xml
-        coverage run run_tests.py --offline
-        coverage xml
+        python run_tests.py --offline
       shell: bash
 
   test_macos:

CONTRIBUTING.rst

@@ -97,11 +97,9 @@ optional dependencies included), plus also style checks using ``pre-commit``
 **The continuous integration checks must pass before your pull request will be
 merged.**
 
-The continuous integration tests collect test coverage information via
-CodeCov: https://codecov.io/github/biopython/biopython/
-
-Ideally the CodeCov checks will also pass, but we currently do not insist on
-this when reviewing pull requests.
+We have previously used CodeCov to track test coverage information, and would
+like to restore this - but historically did not insist their test coverage
+checks passed when reviewing  pull requests.
 
 Contributing to the Biopython Tutorial
 --------------------------------------

README.rst

@@ -16,9 +16,6 @@
 .. image:: https://img.shields.io/github/actions/workflow/status/biopython/biopython/ci.yml?logo=github-actions
    :alt: GitHub workflow status
    :target: https://github.com/biopython/biopython/actions
-.. image:: https://img.shields.io/codecov/c/github/biopython/biopython/master.svg?logo=codecov
-   :alt: Test coverage on CodeCov
-   :target: https://codecov.io/github/biopython/biopython/
 .. image:: http://depsy.org/api/package/pypi/biopython/badge.svg
    :alt: Research software impact on Depsy
    :target: http://depsy.org/package/python/biopython