TST: clean deprecation warnings for xref #19980
xfail some mpl > 2.1.2 tests

 @jorisvandenbossche
cc @GGordonGordon  

would have rather actually changed the usage of ``tsplot`` to the non-deprecated form in all places (except the actual deprecation test), followup PR would be great. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20013?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@fe61299`). [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/20013/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/20013?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #20013   +/-   ##
=========================================
  Coverage          ?    91.7%           
=========================================
  Files             ?      150           
  Lines             ?    49067           
  Branches          ?        0           
=========================================
  Hits              ?    44996           
  Misses            ?     4071           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.08% <ø> (?)` | |
| #single | `41.88% <ø> (?)` | |


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 @jreback sorry, somehow I had in my mind that we didn't use this `tsplot` method at all, which is also the case in the code, but apparently not in the tests ... and didn't check that when merging. 

I personally wouldn't bother with changing the tests to non-deprecated version (it seems the tests already test both), but rather just remove them. @jreback did you open an issue for matplotlib 2.2? As this is unrelated I think to the tsplot deprecation? @jorisvandenbossche no I didn't open an issue for mpl 2.2.2. the package is *only* on conda-forge and I don't think works on mac. just trying to fix the build. not even sure what's wrong. @jreback it are issues with the new matplotlib release, not specifically related to mac. Opened an issue for this: https://github.com/pandas-dev/pandas/issues/20031 the mac issue were existing for those tests yes, i know, I justed wanted to say that the *new* failure is only related to the new mpl release and not specifically to mac. But that's how you skipped it now, so perfect. We should only actually solve it, therefore opened the issue.