Merge branch '10648-milestone-css' into 'master'

Removes EE differences for milestone.scss

See merge request gitlab-org/gitlab-ce!26558

app/assets/stylesheets/pages/milestone.scss

@@ -235,6 +235,7 @@ $status-box-line-height: 26px;
     padding: 0;
   }
 
+  .popover-body,
   .popover-content {
     padding: 0;
   }