The `unit/apikey` directory is removed because it does not contain any
tests. Same for `unit/test_decorators.py`.
The `fixture` module is renamed to the special-name `conftest` [0] so
they are available in all tests without the need to import them. With
that in place, I removed all now unneeded or previously already unused
imports from the tests.
Also removed that wierd `sys.path` bit from `unit/zone/test_admin_apikey.py`,
no idea what that was originally intended for.
[0] https://docs.pytest.org/en/6.2.x/fixture.html#conftest-py-sharing-fixtures-across-multiple-files
