CLN: Remove Categorical.from_array
Deprecated in 0.19.0

xref #13854.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18642?src=pr&el=h1) Report
> Merging [#18642](https://codecov.io/gh/pandas-dev/pandas/pull/18642?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/52fefd50f8bffa493018ba8ff8b8c46b95c94ada?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18642/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/18642?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18642      +/-   ##
==========================================
- Coverage    91.6%   91.58%   -0.02%     
==========================================
  Files         153      153              
  Lines       51253    51250       -3     
==========================================
- Hits        46950    46938      -12     
- Misses       4303     4312       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.44% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.67% <ø> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18642?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/18642/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY2F0ZWdvcmljYWwucHk=) | `95.64% <ø> (-0.02%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18642/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18642/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18642?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/18642?src=pr&el=footer). Last update [52fefd5...3ab8d8f](https://codecov.io/gh/pandas-dev/pandas/pull/18642?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @gfyoung 