Remove labels on the detailed view, as Github just added them

Hi!

Github just changed its discussion view (aka detailed view), and added the labels to it. Hence, with you extension, labels are displayed twice:

![screenshot_130](https://f.cloud.github.com/assets/1727830/2035313/2058b260-8938-11e3-8b3d-9ae6ac2cb0e7.png)

This PR removes the modification of the detailed view, as it is not necessary anymore:

![screenshot_131](https://f.cloud.github.com/assets/1727830/2035328/3b9d879e-8938-11e3-84d0-34d4c41e3b54.png)

Tests were updated, too.