CLN: remove __metaclass__ from code base
- [x] xref #25725 & #26165

Removes uses of ``__metaclass__`` from the code base. After #26165 there was actually only one left.

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26178?src=pr&el=h1) Report
> Merging [#26178](https://codecov.io/gh/pandas-dev/pandas/pull/26178?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/947bd7662afa8b6dc4406ec52cefc39d76d2d6cd?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26178/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26178?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26178      +/-   ##
==========================================
- Coverage   91.98%   91.98%   -0.01%     
==========================================
  Files         175      175              
  Lines       52371    52370       -1     
==========================================
- Hits        48175    48170       -5     
- Misses       4196     4200       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.53% <100%> (-0.01%)` | :arrow_down: |
| #single | `40.71% <100%> (-0.15%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26178?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/computation/engines.py](https://codecov.io/gh/pandas-dev/pandas/pull/26178/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tcHV0YXRpb24vZW5naW5lcy5weQ==) | `88.33% <100%> (-0.2%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26178/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26178/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.9% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26178?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/26178?src=pr&el=footer). Last update [947bd76...fa898b0](https://codecov.io/gh/pandas-dev/pandas/pull/26178?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks @topper-123 