Remove default message from conditional module

A message can be added in the XML <conditional> tag, ex: 

```
<conditional sources="i4x://THE/COURSE/TRIPLE/######" message="This message is editable in the corresponding conditional file for the vertical" correct="True">
    <html url_name="######"/>
    <problem url_name="######"/>
</conditional>
```

Example of where the message appears, and where the other message is ugly:

![screen shot 2014-05-07 at 2 07 37 pm](https://cloud.githubusercontent.com/assets/3364609/2908803/bfa2d64e-d62b-11e3-80d1-6c2cef829758.png)