BUG: Dont add None to plot legend.
Closes https://github.com/pydata/pandas/issues/8491

Building the docs now to check that everything looks ok.

Seems like the default for the `legend` argument to `Series.plot` got switched in that plotting cleanup PR that merged stuff between DataFrame.plot and Series.plot.
 Maybe the whatsnew is not really needed, as this was not a bug in the previous released version (or add the issue number to the whatsnew entry of the clean-up)
 Right again. I removed the release notes entry.
 thanks @TomAugspurger
 @TomAugspurger I just noticed it isn't solved for all plots. See eg the the third plot on the doc page: http://pandas-docs.github.io/pandas-docs-travis/visualization.html#basic-plotting-plot
 hmm, no None label for me.  This is that 3rd plot from a local build.

![df_plot_xy](https://cloud.githubusercontent.com/assets/1312546/4802379/05393e10-5e43-11e4-98db-887ca07626d8.png)

Do you get the None label locally?
 Yes, I also get it locally (both on linux -> official docs are built there, as now on WIndows):

```
pandas: 0.15.0-16-g7012d71
numpy: 1.9.0
IPython: 2.1.0
matplotlib: 1.4.0
```
 Ok, well I have a windows machine at work now. I'll check it out. Thanks.
