Remove comment field from fact check form

* When submitting to fact check the comments aren’t used, the field also obscures the very important “custom message” field. At worst the two are confused. The comment also displayed as a required field, it isn't.
* Remove comments altogether and make the custom message field bigger now there’s more space.

## Before
![screen shot 2014-10-09 at 12 44 21](https://cloud.githubusercontent.com/assets/319055/4575636/cf34faea-4fa9-11e4-8184-ef18777f48ca.png)

## After
![screen shot 2014-10-09 at 12 43 59](https://cloud.githubusercontent.com/assets/319055/4575637/d247d00e-4fa9-11e4-90b2-d7a650fc2354.png)