Remove invalid HTML in proposal notifications

This HTML wasn't valid because it was a <span> containing the <div
class="reply"> element and it wasn't needed because there aren't any
flag actions in proposal notifications.

app/views/proposals/_notifications.html.erb

@@ -13,9 +13,7 @@
           <p class="more-info"><%= notification.created_at.to_date %></p>
           <%= simple_format sanitize_and_auto_link(notification.body), {}, sanitize: false %>
 
-          <span class="js-flag-actions">
           <%= render "proposal_notifications/actions", notification: notification %>
-          </span>
         </div>
       <% end %>
     </div>