CLN: Removed trellis rplot
xref https://github.com/pydata/pandas/pull/9357.

Title is self-explanatory.

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13855?src=pr) is 85.30% (diff: 100%)

> No coverage report found for **master** at a7f7e1d.
> 
> Powered by [Codecov](https://codecov.io?src=pr). Last update [a7f7e1d...9666d4d](https://codecov.io/gh/pydata/pandas/compare/a7f7e1d18baa36afe9317aa48fbcf170b0375318...9666d4d119e95882eb4b97338ce0b6677969f80d?src=pr)
 I would just remove that entire doc section (or maybe leave in the note it was removed, and put a link to the doc section of the previous release). 
If you would keep it, you have to include the png files.
 @jorisvandenbossche : I updated the documentation to include a link to the documentation in `0.18.1`.  I'm not sure that that is the right link though (in terms of format).  How can you even see old versions of the documentation online?
 http://pandas.pydata.org/pandas-docs/version/0.18.1/

You can access it from the front page (pandas.pydata.org)
 Okay, good to know!  Updated the documentation, so ready to merge if there are no other concerns.
 is there an issue for this? can you reference at the top.
 There is no associated issue for it.
 sure there is; updated.
 Where?  I don't see any issue for removing this.
 no we reference the issue that deprecated this, which is what I did.
 Ah, I see.  Made the doc change FYI.
 thanks!
