CLN: Remove the engine parameter in CSVFormatter and to_csv
Title is self-explanatory.

Internal code and #6581 indicate that this was long overdue.

see #11274 this was actually just deprecated in 0.17.1 (even though it _said_ 0.13).
 @gfyoung Master is now targeted for 0.19.0, so this can go in. Can you move the whatsnew note to the correct file?
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13419?src=pr) is **84.32%**

> Merging [#13419](https://codecov.io/gh/pydata/pandas/pull/13419?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **0.01%**

``` diff
@@             master     #13419   diff @@
==========================================
  Files           138        138          
  Lines         51157      51083    -74   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          43131      43076    -55   
+ Misses         8026       8007    -19   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [5701c69...ddd6cd2](https://codecov.io/gh/pydata/pandas/compare/5701c69369264f3aa6f571384602ceec1133dabc...ddd6cd2e367543ec3fc77a3cf0b34d8b7290e21e?src=pr)
 @jreback , @jorisvandenbossche : Travis is passing, so ready to merge if there are no other concerns.
 lgtm. ping on green.
 @jreback : Travis is giving the green light.  Ready to merge if there are no other concerns.
 @gfyoung yes, merging shortly. 
 thanks @gfyoung 
