Remove codecov from dependency files (#1328)

Remove `codecov` from dependency files. See https://docs.codecov.com/docs/deprecated-uploader-migration-guide\#python-uploader

Author: abhinavsingh

requirements-testing.txt

@@ -10,7 +10,6 @@ pytest-asyncio==0.16.0
 autopep8==1.6.0
 mypy==0.971
 py-spy==0.3.12
-codecov==2.1.12
 tox==3.25.1
 mccabe==0.6.1
 pylint==2.13.7