Remove `public_trial` field from repository byline.

As per [specification](https://my.teamraum.com/workspaces/onegov-gever-innovation-session/improvement-proposals/ogip6-umsetzung-offentlichkeitsgesetz/view), the `public_trial` field should not show up in the byline of repository folders any more. This pull request removes the `public_trial` field from the already customized repository folder byline:

---

#### Before

![repo_folder_byline_before](https://cloud.githubusercontent.com/assets/405124/3660554/ba5fb86e-11b8-11e4-8406-c6a074a70463.png)

---

#### After

![repo_folder_byline_after](https://cloud.githubusercontent.com/assets/405124/3660556/bf160502-11b8-11e4-9bfb-18dbeb5894cb.png)

@phgross please review.