Fix root cause of warnings in tests

[alessandrofelder]

Currently, we ignore some warnings in our tests via pytest.ini settings:

filterwarnings =
    ignore:distutils Version classes are deprecated:DeprecationWarning
    ignore:The hookimpl CovPlugin.pytest_.* uses old-style configuration options:pytest.PytestDeprecationWarning

Instead of ignoring some warnings with a pytest filter, we should avoid them happening in the first place.

[alessandrofelder]

Related to #30 .

[adamltyson]

Closing, as we no longer filter any warnings.