CLN: Remove unused variable in test_reshape.py
Title is self-explanatory.

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22573?src=pr&el=h1) Report
> Merging [#22573](https://codecov.io/gh/pandas-dev/pandas/pull/22573?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/550a5cae1ab7fd2eb49273ab281b16e8a37966c5?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/22573/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22573?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22573   +/-   ##
=======================================
  Coverage   92.04%   92.04%           
=======================================
  Files         169      169           
  Lines       50787    50787           
=======================================
  Hits        46745    46745           
  Misses       4042     4042
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <ø> (ø)` | :arrow_up: |
| #single | `42.29% <ø> (ø)` | :arrow_up: |


------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
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