CLN: Old helper functions
- [x] closes #21838
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

It appears that these functions were helpers at one point in the past, but they don't appear anywhere in the codebase now (and are not publicly documented).

I _think_ they are safe to blow away, although they exist the public namespace. 
Tests.io.test_sql needs format Although the name makes grepping for it pretty much impossible # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22104?src=pr&el=h1) Report
> Merging [#22104](https://codecov.io/gh/pandas-dev/pandas/pull/22104?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/0b7a08b70444056f964bb636a74ac41ca0058d37?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22104/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22104?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22104      +/-   ##
==========================================
+ Coverage   92.06%   92.06%   +<.01%     
==========================================
  Files         170      170              
  Lines       50705    50691      -14     
==========================================
- Hits        46680    46669      -11     
+ Misses       4025     4022       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.47% <100%> (ø)` | :arrow_up: |
| #single | `42.31% <100%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22104?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/util.py](https://codecov.io/gh/pandas-dev/pandas/pull/22104/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS91dGlsLnB5) | `100% <ø> (+9.67%)` | :arrow_up: |
| [pandas/core/tools/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/22104/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvdG9vbHMvZGF0ZXRpbWVzLnB5) | `84.78% <100%> (-0.44%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22104?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/22104?src=pr&el=footer). Last update [0b7a08b...d88151f](https://codecov.io/gh/pandas-dev/pandas/pull/22104?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @mroeschke 