 TST/CLN: Remove more Panel tests
cc @jbrockmendel 
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=h1) Report
> Merging [#25550](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d10bbce349b293e9f753d799cd2ad032d5ec7333?src=pr&el=desc) will **decrease** coverage by `0.48%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25550/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25550      +/-   ##
==========================================
- Coverage   91.75%   91.27%   -0.49%     
==========================================
  Files         173      173              
  Lines       52960    52960              
==========================================
- Hits        48595    48337     -258     
- Misses       4365     4623     +258
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.84% <ø> (-0.49%)` | :arrow_down: |
| #single | `41.71% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `38.56% <0%> (-33.19%)` | :arrow_down: |
| [pandas/core/indexing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhpbmcucHk=) | `90.88% <0%> (-1.41%)` | :arrow_down: |
| [pandas/core/internals/managers.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL21hbmFnZXJzLnB5) | `93.92% <0%> (-0.92%)` | :arrow_down: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `93.64% <0%> (-0.53%)` | :arrow_down: |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `91.63% <0%> (-0.14%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25550?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/25550?src=pr&el=footer). Last update [d10bbce...0c438d9](https://codecov.io/gh/pandas-dev/pandas/pull/25550?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/25550?src=pr&el=h1) Report
> Merging [#25550](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d10bbce349b293e9f753d799cd2ad032d5ec7333?src=pr&el=desc) will **decrease** coverage by `0.48%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25550/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25550      +/-   ##
==========================================
- Coverage   91.75%   91.27%   -0.49%     
==========================================
  Files         173      173              
  Lines       52960    52960              
==========================================
- Hits        48595    48337     -258     
- Misses       4365     4623     +258
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.84% <ø> (-0.49%)` | :arrow_down: |
| #single | `41.71% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `38.56% <0%> (-33.19%)` | :arrow_down: |
| [pandas/core/indexing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhpbmcucHk=) | `90.88% <0%> (-1.41%)` | :arrow_down: |
| [pandas/core/internals/managers.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL21hbmFnZXJzLnB5) | `93.92% <0%> (-0.92%)` | :arrow_down: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `93.64% <0%> (-0.53%)` | :arrow_down: |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/25550/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `91.63% <0%> (-0.14%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25550?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/25550?src=pr&el=footer). Last update [d10bbce...0c438d9](https://codecov.io/gh/pandas-dev/pandas/pull/25550?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Lgtm thanks @simonjayhawkins 