OSL Example: redundant cell in example removed

Noticed that code cells 3 and 4 are the same for the [ordinary least squares example](http://statsmodels.sourceforge.net/devel/examples/notebooks/generated/ols.html)

![osl_redundant_cell](https://cloud.githubusercontent.com/assets/2342749/3077009/8b2a2a3a-e40d-11e3-8765-6cc3adf9d814.png)