CLN: Remove Panel benchmarks
xref #25632

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25646?src=pr&el=h1) Report
> Merging [#25646](https://codecov.io/gh/pandas-dev/pandas/pull/25646?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f88613929d6c83952cb5a6bf70678a78be480baa?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/25646/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25646?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25646      +/-   ##
==========================================
- Coverage   91.26%   91.26%   -0.01%     
==========================================
  Files         173      173              
  Lines       52968    52968              
==========================================
- Hits        48340    48339       -1     
- Misses       4628     4629       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.83% <ø> (ø)` | :arrow_up: |
| #single | `41.71% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25646?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25646/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `87.57% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25646?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/25646?src=pr&el=footer). Last update [f886139...00102b8](https://codecov.io/gh/pandas-dev/pandas/pull/25646?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/25646?src=pr&el=h1) Report
> Merging [#25646](https://codecov.io/gh/pandas-dev/pandas/pull/25646?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/10173821965fa65654b172891b2102a8426132ca?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25646/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25646?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25646   +/-   ##
=======================================
  Coverage   91.24%   91.24%           
=======================================
  Files         172      172           
  Lines       52967    52967           
=======================================
  Hits        48332    48332           
  Misses       4635     4635
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.82% <ø> (ø)` | :arrow_up: |
| #single | `41.74% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25646?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/25646?src=pr&el=footer). Last update [1017382...b4917f9](https://codecov.io/gh/pandas-dev/pandas/pull/25646?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hmm the ASV doc failures looks to be the same issue as https://github.com/pandas-dev/pandas/issues/24839 potentially.  Agreed. Additionally the failing benchmarks are not related to the Panel changes.

Merging. 