Remove bottom border from Issuable titles

Prevent duplicate lines when issue/merge request is empty.

Empty MR

Empty Issue

app/assets/stylesheets/pages/detail_page.scss

@@ -20,10 +20,10 @@
 
 .detail-page-description {
   .title {
-    margin: 0;
-    font-size: 2em;
     color: $gl-gray-dark;
+    font-size: 2em;
     padding: 0;
+    margin: 0;
   }
 
   .description {