VIS: plot with `use_index=False` shouldn't plot the index name

Fixes #8558. As far as I can tell the two plot types where this applies are line and bar plots, if there any others they should also be easy to fix. Bar and line plots no longer include the index name:

```python
import pandas as pd
from pandas import Series
import matplotlib.pyplot as plt

s = Series([1, 2, 3], index=['a', 'b', 'c'])
s.index.name = 'The Index'

ax = s.plot(use_index=False)
plt.show()
```
￼
![image](https://cloud.githubusercontent.com/assets/1460294/5041001/6095c37e-6c0c-11e4-86ca-8e1c4ec83b3c.png)


```python
ax2 = s.plot(kind='bar', use_index=False)
plt.show()
```


![image](https://cloud.githubusercontent.com/assets/1460294/5041003/657a45d6-6c0c-11e4-92a2-642e5df917a0.png)