CategoricalAccessor.categorical removed in 0.24.0rc1
Previously, CategoricalAccessor set `.categorical` in `__init__`. I don't think this was intended to be the way to access things like `.ordered`, but it wasn't prefixed with an underscore, so we should deprecate before removing

0.23.4

```python
In [11]: pd.Series(['a', 'b'], dtype='category').cat.categorical.ordered
Out[11]: False
```

0.24.0rc1

```python
In [3]: pd.Series(['a', 'b'], dtype='category').cat.categorical.ordered
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-3-e5c7f0300480> in <module>
----> 1 pd.Series(['a', 'b'], dtype='category').cat.categorical.ordered

AttributeError: 'CategoricalAccessor' object has no attribute 'categorical'
```

We can deprecate with

```python
def categorical(self):
    warnings.warn(...)
    return self._parent
```

in https://github.com/pandas-dev/pandas/blob/33f91d8f9f2e84f2b5f3ac3f0481b691c977c427/pandas/core/arrays/categorical.py#L2472

We should do the same for `.index` and `.name`.