CLN: Removed DataFrame.to_wide
`to_wide` was deprecated since 2011 (https://github.com/pydata/pandas/commit/1134c9f6c40398d8eba37c312c88ce294e31c6c5)

xref https://github.com/pydata/pandas/issues/13777

No tests for this deprecation beforehand to remove :disappointed: 

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14039?src=pr) is 85.25% (diff: 100%)

> Merging [#14039](https://codecov.io/gh/pydata/pandas/pull/14039?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #14039   diff @@
==========================================
  Files           139        139          
  Lines         50380      50379     -1   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          42953      42952     -1   
  Misses         7427       7427          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [453bc26...7879d54](https://codecov.io/gh/pydata/pandas/compare/453bc26e07ebbfea33dda9ff2f4efab683718506...7879d549601f2f7b1b3f37dd96d612f296f3577e?src=pr)
 lgtm. ping on green.
 Let's leave that for another PR :-) (I/we will do a full read through of the whatsnew file anyway)
 @gfyoung Thanks!
