CLN: remove sample_time attributes from benchmarks
Very minor benchmark cleanup now that I was on it...

These attributes appear to have been brought in by direct replacement of a
deprecated ASV attribute goal_time -> sample_time, but the two have
different semantics (the value sample_time=0.2 is 20x the default).
Increasing this from the default value is probably not necessary and
increases runtime (here 3min vs 17min for rolling.*), so it's better to restore it to defaults.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=h1) Report
> Merging [#26598](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7f318658b92155678b31780722277d1f8c8df569?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26598/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26598      +/-   ##
==========================================
- Coverage   91.84%   91.84%   -0.01%     
==========================================
  Files         174      174              
  Lines       50644    50644              
==========================================
- Hits        46516    46512       -4     
- Misses       4128     4132       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.37% <ø> (ø)` | :arrow_up: |
| #single | `41.71% <ø> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26598/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/26598/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26598?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/26598?src=pr&el=footer). Last update [7f31865...dc51708](https://codecov.io/gh/pandas-dev/pandas/pull/26598?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/26598?src=pr&el=h1) Report
> Merging [#26598](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7f318658b92155678b31780722277d1f8c8df569?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26598/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26598      +/-   ##
==========================================
- Coverage   91.84%   91.84%   -0.01%     
==========================================
  Files         174      174              
  Lines       50644    50644              
==========================================
- Hits        46516    46512       -4     
- Misses       4128     4132       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.37% <ø> (ø)` | :arrow_up: |
| #single | `41.71% <ø> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26598/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/26598/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26598?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/26598?src=pr&el=footer). Last update [7f31865...dc51708](https://codecov.io/gh/pandas-dev/pandas/pull/26598?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @pv 

always welcome comments on the asv structure :->