TST: Make encoded sep check more locale sensitive
Follow-up to #14120 to make the `sep` check more locale sensitive.  Closes #14140.

ok looks fine
ping on all green 
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14161?src=pr) is 85.24% (diff: 50.00%)

> Merging [#14161](https://codecov.io/gh/pydata/pandas/pull/14161?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #14161   diff @@
==========================================
  Files           140        140          
  Lines         50549      50555     +6   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43090      43095     +5   
- Misses         7459       7460     +1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [02df7b6...4f3d833](https://codecov.io/gh/pydata/pandas/compare/02df7b683734cafd87ad7b5920dd2a628521999c...4f3d833d7d4a618e9714ac4efe03ab4f2fdce912?src=pr)
 doesn't appear to fix the issue. https://github.com/pydata/pandas/commit/1a8273cfa9d835fcc377a020c16bc6d55a9ad98b skipping for now (pls reverse in your commit)
 @jreback : Okay, thanks for letting me know.  I might need to do some hackish commits to debug what Appveyor is doing with regards to locale.
 @jreback : Just as I thought.  The system encoding used on Appveyor Python 3.5 is one that will actually encode the separator properly (see <a href="https://ci.appveyor.com/project/jreback/pandas-465/build/1.0.1006/job/4idc6de9oawlgutm">here</a>).  I can also confirm on my local Windows machine.

The test is flaky across Appveyor and Travis, so I think it is best to remove or disable.
 fine to remove/disable
 @jreback : Removed the test.  Ready to merge if there are no other concerns.
 thanks
