Remove placeholder of on-page description field in facia-tool

A quick one.
If the on-page description field is empty, don't display the placeholder text.
![screen shot 2014-09-30 at 17 05 18](https://cloud.githubusercontent.com/assets/1492162/4461602/b43d2d60-48bb-11e4-8b84-32c8292c1abc.png)