Remove unused get methods that would raise AttributeError if called
 - [x] closes #17159
 - [ ] tests added / passed
 - [x] passes ``git diff upstream/master -u -- "*.py" | flake8 --diff``
 - [ ] whatsnew entry

@jbrockmendel : LGTM, though I will wait to see if you can remove more based on discussion in #17159. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17169?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@9b07ef4`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17169/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17169?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #17169   +/-   ##
=========================================
  Coverage          ?   90.98%           
=========================================
  Files             ?      162           
  Lines             ?    49499           
  Branches          ?        0           
=========================================
  Hits              ?    45039           
  Misses            ?     4460           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.76% <ø> (?)` | |
| #single | `40.27% <ø> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17169?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/17169?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `94.24% <ø> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17169?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17169?src=pr&el=footer). Last update [9b07ef4...51f041b](https://codecov.io/gh/pandas-dev/pandas/pull/17169?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 I just pushed a commit to remove an unnecessary import.  The other issue I don't expect to get to anytime soon. @jbrockmendel Thanks!