Remove check icon from merged MRs

Now that GitLab CI exposes the status of each MR in the MR page it seems "redundant" to have an extra icon next to the CI statuses.

The "downside" is with people that don't use CI and don't see the statuses, but I don't think that this is that big a change that would miss to anyone.

\cc @dzaporozhets @creamzy 

How it looks now:

![screenshot-gitlab_com_2015-12-10_20-49-53](/uploads/414dcb5131eab2d9518dc77019116c96/screenshot-gitlab_com_2015-12-10_20-49-53.png)


See merge request !2059