CLN: Replaced package list with find_packages
- [X] closes #18535 
- [ ] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

As far as local testing goes, I built source distributions using py27 and py36. Compared to HEAD, the generated distributions were practically identical. Technically they were off by a size of around 100 bytes, but I was getting that same variation when generating clean built distributions just on HEAD alone. Running a recursive diff showed some slight differences in the ``.so`` files, but given I saw that variation without making any changes I think it is OK.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=h1) Report
> Merging [#18632](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/2c903d594299b2441d4742e777a10e8c76557386?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18632/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18632      +/-   ##
==========================================
- Coverage   91.59%   91.57%   -0.02%     
==========================================
  Files         155      155              
  Lines       51255    51255              
==========================================
- Hits        46949    46939      -10     
- Misses       4306     4316      +10
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.44% <ø> (-0.01%)` | :arrow_down: |
| #single | `40.67% <ø> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `81.82% <0%> (-0.2%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.68% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18632?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/18632?src=pr&el=footer). Last update [2c903d5...97654b7](https://codecov.io/gh/pandas-dev/pandas/pull/18632?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/18632?src=pr&el=h1) Report
> Merging [#18632](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a7f6714aa24ff64b49b249d76e59ede36ef04116?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/18632/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18632      +/-   ##
==========================================
+ Coverage   91.57%   91.57%   +<.01%     
==========================================
  Files         153      153              
  Lines       51257    51257              
==========================================
+ Hits        46937    46940       +3     
+ Misses       4320     4317       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.44% <ø> (+0.02%)` | :arrow_up: |
| #single | `40.68% <ø> (-0.11%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/window.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvd2luZG93LnB5) | `96.31% <0%> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/18632/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.52% <0%> (+1.73%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18632?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/18632?src=pr&el=footer). Last update [a7f6714...04e85f5](https://codecov.io/gh/pandas-dev/pandas/pull/18632?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 can you rebase this once again. The AppVeyor failure is for a plotting test and does not appear to be related to any change made here  thanks @WillAyd 