This was added when we first migrated to pytest, but pytest is now
complaining that this setting is unknown.
Since it doesn't do anything, lets remove it
With this change you should be able to simply run `pytest` to run all the tests in the main airflow directory.
This consist of two changes:
* moving pytest.ini to the main airflow directory
* skipping collecting kubernetes tests when ENV != kubernetes
Ash Berlin-Taylor
Jarek Potiuk
Kamil Breguła
Andrey Klochkov