CLN: remove __unicode__ from pandas.core.dtypes
- [x] xref #25725

Removes use of ``__unicode__`` from the pandas.core.dtypes namespace.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=h1) Report
> Merging [#26415](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ff4437eb3b27440ea2304a8613369ebec0b8b72a?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `85.71%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26415/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26415      +/-   ##
==========================================
- Coverage   91.69%   91.68%   -0.01%     
==========================================
  Files         174      174              
  Lines       50739    50737       -2     
==========================================
- Hits        46524    46518       -6     
- Misses       4215     4219       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.19% <85.71%> (-0.01%)` | :arrow_down: |
| #single | `41.18% <85.71%> (-0.16%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/26415/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `96.65% <85.71%> (-0.02%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26415/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/26415/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.02% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26415?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/26415?src=pr&el=footer). Last update [ff4437e...c10ff78](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=h1) Report
> Merging [#26415](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ff4437eb3b27440ea2304a8613369ebec0b8b72a?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `85.71%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26415/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26415      +/-   ##
==========================================
- Coverage   91.69%   91.68%   -0.01%     
==========================================
  Files         174      174              
  Lines       50739    50737       -2     
==========================================
- Hits        46524    46518       -6     
- Misses       4215     4219       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.19% <85.71%> (-0.01%)` | :arrow_down: |
| #single | `41.18% <85.71%> (-0.16%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/26415/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `96.65% <85.71%> (-0.02%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26415/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/26415/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.02% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26415?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/26415?src=pr&el=footer). Last update [ff4437e...c10ff78](https://codecov.io/gh/pandas-dev/pandas/pull/26415?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @topper-123 imagine we have a these