remove unnecessary check_output copy/pasted code
It isn't clear to me why this is needed.  Maybe the CI will fail, in which case I'll just add a comment in the code explaining why it is needed.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=h1) Report
> Merging [#25755](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/707c7201a744c48c835f719421e47480beee2184?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/25755/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25755      +/-   ##
==========================================
+ Coverage   91.25%   91.26%   +<.01%     
==========================================
  Files         172      172              
  Lines       52977    52965      -12     
==========================================
- Hits        48342    48336       -6     
+ Misses       4635     4629       -6
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.83% <100%> (ø)` | :arrow_up: |
| #single | `41.73% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25755/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `89.44% <100%> (+0.46%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25755?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/25755?src=pr&el=footer). Last update [707c720...c4f7257](https://codecov.io/gh/pandas-dev/pandas/pull/25755?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/25755?src=pr&el=h1) Report
> Merging [#25755](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/707c7201a744c48c835f719421e47480beee2184?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/25755/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25755      +/-   ##
==========================================
+ Coverage   91.25%   91.26%   +<.01%     
==========================================
  Files         172      172              
  Lines       52977    52965      -12     
==========================================
- Hits        48342    48336       -6     
+ Misses       4635     4629       -6
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.83% <100%> (ø)` | :arrow_up: |
| #single | `41.73% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25755/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `89.44% <100%> (+0.46%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25755?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/25755?src=pr&el=footer). Last update [707c720...c4f7257](https://codecov.io/gh/pandas-dev/pandas/pull/25755?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!