launch: prevent dismissed welcome affecting mobile

Flexbox would provide the empty <div> some space in our mobile layout.
This replaces the div with null.

pkg/interface/launch/src/js/components/welcome.js

@@ -33,7 +33,7 @@ export class Welcome extends Component {
         </p>
       </div>
     )
-    : ( <div/>)
+    : ( null)
   }
 }