CLN: Unreachable code, Boolean comparison, duplicate functions
Breaking up #21974.

This batch is:

- Unreachable code
- Redefined function (in asv)
- Boolean equality comparison

LGTM.  

@jorisvandenbossche IIRC you wanted to keep numpydoc changes separate from others? > IIRC you wanted to keep numpydoc changes separate from others?

Yes, numpydoc is vendored. So if we want to make changes to it, it should be done upstream. lgtm. not sure by @jorisvandenbossche comments 

ok to make the numpydoc change here and push upstream as well?  No, no reason to do it here. That only makes updating our version with upstream afterwards harder. @mroeschke ok then if you'd pull the numpydoc changes out # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21985?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@27ebb3e`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21985/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/21985?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #21985   +/-   ##
=========================================
  Coverage          ?   91.97%           
=========================================
  Files             ?      166           
  Lines             ?    50328           
  Branches          ?        0           
=========================================
  Hits              ?    46287           
  Misses            ?     4041           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.36% <ø> (?)` | |
| #single | `42.23% <ø> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21985?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/21985/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9wZXJpb2QucHk=) | `93.39% <ø> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21985?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/21985?src=pr&el=footer). Last update [27ebb3e...1a5a486](https://codecov.io/gh/pandas-dev/pandas/pull/21985?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks!