CLN: Remove unused method
- [y] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

This method isn't used anywhere in the codebase, good to delete?
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22321?src=pr&el=h1) Report
> Merging [#22321](https://codecov.io/gh/pandas-dev/pandas/pull/22321?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/601d71fcfa9081fa88e5c20148972cd766396cd7?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22321/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/22321?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22321      +/-   ##
==========================================
+ Coverage   92.08%   92.08%   +<.01%     
==========================================
  Files         169      169              
  Lines       50706    50703       -3     
==========================================
- Hits        46691    46689       -2     
+ Misses       4015     4014       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.49% <ø> (ø)` | :arrow_up: |
| #single | `42.33% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22321?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/22321/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `95.41% <ø> (+0.07%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22321?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/22321?src=pr&el=footer). Last update [601d71f...ac64c8e](https://codecov.io/gh/pandas-dev/pandas/pull/22321?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks! improved coverage!