DEPR: Remove pandas.np
Not sure if it was added intentionally, but it's possible to call numpy with the `np` attribute of the pandas module:
```python
import pandas
x = pandas.np.array([1, 2, 3])
```
While this is not documented, I've seen couple of places suggesting this as a "trick" to avoid importing numpy directly.

I personally find this hacky, and I think should be removed. 