DEPR: Add deprecated index attribute names to deprecation list
In ipython, when you press tab (e.g. ``idx.<tab>``) a long list of deprecations shows up:

```
C:\Users\TP\Miniconda3\envs\pandas-dev\lib\site-packages\jedi\evaluate\compiled\__init__.py:328: FutureWarning: Int64Index.base is deprecated and will be removed in a future version
  getattr(obj, name)
C:\Users\TP\Miniconda3\envs\pandas-dev\lib\site-packages\jedi\evaluate\compiled\__init__.py:328: FutureWarning: Int64Index.data is deprecated and will be removed in a future version
  getattr(obj, name)
C:\Users\TP\Miniconda3\envs\pandas-dev\lib\site-packages\jedi\evaluate\compiled\__init__.py:328: FutureWarning: Int64Index.flags is deprecated and will be removed in a future version
  getattr(obj, name)
C:\Users\TP\Miniconda3\envs\pandas-dev\lib\site-packages\jedi\evaluate\compiled\__init__.py:328: FutureWarning: Int64Index.itemsize is deprecated and will be removed in a future version
  getattr(obj, name)
C:\Users\TP\Miniconda3\envs\pandas-dev\lib\site-packages\jedi\evaluate\compiled\__init__.py:328: FutureWarning: Int64Index.strides is deprecated and will be removed in a future version
  getattr(obj, name)
```

With this PR we avoid getting that list of deprecations in iPython.

I'm not sure if/where this should go in the whatsnew document.
Not able to locate t. Where its name? # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21125?src=pr&el=h1) Report
> Merging [#21125](https://codecov.io/gh/pandas-dev/pandas/pull/21125?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/bc37ea2e05019a89adaa48159b220483598d1898?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21125/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/21125?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21125   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
=======================================
  Files         153      153           
  Lines       49499    49499           
=======================================
  Hits        45460    45460           
  Misses       4039     4039
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <100%> (ø)` | :arrow_up: |
| #single | `41.88% <100%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21125?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/accessor.py](https://codecov.io/gh/pandas-dev/pandas/pull/21125/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYWNjZXNzb3IucHk=) | `98.71% <100%> (ø)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21125?src=pr&el=footer). Last update [bc37ea2...a54b416](https://codecov.io/gh/pandas-dev/pandas/pull/21125?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 I think this is the test @jreback is referring to:
https://github.com/pandas-dev/pandas/blob/e033c0616158d3ba974456b4f84810492936b1fe/pandas/tests/series/test_api.py#L465-L474

There are also instances of this test (same name) in `frame\test_api.py` and `categorical\test_warnings.py` test added. Is the location ok? BTW, @jschendel in line 474 in the ``test_api.py`` file you showed

https://github.com/pandas-dev/pandas/blob/e033c0616158d3ba974456b4f84810492936b1fe/pandas/tests/series/test_api.py#L472-L474

I think ``list(ip.Completer.completions('s.', 1))`` should be ``list(ip.Completer.completions('s.', 2))`` in order to produce the warnings, do you not agree? With ``1`` the tab is pressed after ``'s'`` which is too early. looks ok. can you add a whatsnew note (0.23.1) green. thanks!