CLN: ASV reshape
Flake8'd and simplified setups where available.

```
$ asv dev -b ^reshape
· Discovering benchmarks
· Running 9 total benchmarks (1 commits * 1 environments * 9 benchmarks)
[  0.00%] ·· Building for existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[  0.00%] ·· Benchmarking existing-py_home_matt_anaconda_envs_pandas_dev_bin_python
[ 11.11%] ··· Running reshape.Melt.time_melt_dataframe                   7.27ms
[ 22.22%] ··· Running reshape.Pivot.time_reshape_pivot_time_series        441ms
[ 33.33%] ··· Running reshape.PivotTable.time_pivot_table                46.0ms
[ 44.44%] ··· Running reshape.SimpleReshape.time_stack                   6.73ms
[ 55.56%] ··· Running reshape.SimpleReshape.time_unstack                 6.05ms
[ 66.67%] ··· Running reshape.SparseIndex.time_unstack                   2.76ms
[ 77.78%] ··· Running reshape.Unstack.time_full_product                   254ms
[ 88.89%] ··· Running reshape.Unstack.time_without_last_row               477ms
[100.00%] ··· Running reshape.WideToLong.time_wide_to_long_big            378ms
```
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18944?src=pr&el=h1) Report
> Merging [#18944](https://codecov.io/gh/pandas-dev/pandas/pull/18944?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/cdebcf374598e9141df7dc23bc75c9528e92c004?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18944/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18944?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18944      +/-   ##
==========================================
+ Coverage   91.59%   91.59%   +<.01%     
==========================================
  Files         150      150              
  Lines       48959    48959              
==========================================
+ Hits        44843    44845       +2     
+ Misses       4116     4114       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.96% <ø> (ø)` | :arrow_up: |
| #single | `41.13% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18944?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/18944/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.9% <0%> (+0.21%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18944?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/18944?src=pr&el=footer). Last update [cdebcf3...3d8e4e9](https://codecov.io/gh/pandas-dev/pandas/pull/18944?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!