Remove unused files from src/klib
De-couple ujson from numpy_helper
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19415?src=pr&el=h1) Report
> Merging [#19415](https://codecov.io/gh/pandas-dev/pandas/pull/19415?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8a7aca9eda989243fedae4ef525ddef4511ab241?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19415/graphs/tree.svg?width=650&src=pr&height=150&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/19415?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19415      +/-   ##
==========================================
+ Coverage   91.62%   91.65%   +0.02%     
==========================================
  Files         150      150              
  Lines       48729    48729              
==========================================
+ Hits        44649    44661      +12     
+ Misses       4080     4068      -12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.02% <ø> (+0.02%)` | :arrow_up: |
| #single | `41.75% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19415?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19415/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.95% <0%> (+1.73%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19415?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/19415?src=pr&el=footer). Last update [8a7aca9...fac58f2](https://codecov.io/gh/pandas-dev/pandas/pull/19415?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!