Fix: remove location when publisher is cleared by user

When a post being written and containing a location is cleared (clicking the cross at the top right of the publisher), the location frame is not removed : 
![before](https://f.cloud.github.com/assets/2453133/1846396/a00297f4-75f3-11e3-9420-5fb1a15346e7.png)

This PR automatically removes the location in this case.