Remove check icon from merged requests

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.

app/views/projects/merge_requests/_merge_request.html.haml

@@ -5,7 +5,6 @@
     %ul.controls.light
       - if merge_request.merged?
         %li
-          = icon('check')
           MERGED
       - elsif merge_request.closed?
         %li