TST: Clean pytest fixtures
* Move sparsely used fixtures to where they are used (in the file or inlined)
* Removed fixtures that had no use in `conftest.py` files
if you're on fixture patrol, we have a couple of 

```
pytestmark = pytest.mark.parametrize("ext", [".ods"])
pytestmark = pytest.mark.parametrize("ext", [".xlsx"])
```

that look pretty clearly wrong (not