Remove codecov dependency to fix pip install issue

On April 12, 2023 codecov package was removed from pypi repository.
It makes that installing dependencies with pip command failed. As
result you can't contribute  to pyinfra. This commit fix pip
installation issue.
See also codecov explaination of the situation
https://about.codecov.io/blog/message-regarding-the-pypi-package/

setup.py

@@ -43,7 +43,6 @@
     'pytest==7.2.0 ; python_version > "3.6"',
     'coverage==6.5 ; python_version > "3.6"',
     "pytest-cov==4.0.0",
-    "codecov==2.1.12",
     # Formatting & linting
     "black==22.3.0",
     "isort==5.10.1",