Backport empty panel heading from EE related issues

See
https://gitlab.com/gitlab-org/gitlab-ee/commit/4b5a1c9a6570d70cd3e16b3c1d3c2ec0471f46eb#777d5694836def44d2a73f1c7590aea20aed6c22_35_35

From MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1797/

app/assets/stylesheets/framework/panels.scss

@@ -34,6 +34,10 @@
     }
   }
 
+  .panel-empty-heading {
+    border-bottom: 0;
+  }
+
   .panel-body {
     padding: $gl-padding;