remove obsolete header_tags

this is most likely a copy & paste artifact:

commit 0eba424adf
Date:   Tue Jan 21 11:45:09 2014 +0100

    did some copy pasting to get configs crud to look like other admin
sections.

app/views/export_card_configurations/index.html.erb

@@ -24,9 +24,6 @@ See doc/COPYRIGHT.md for more details.
 
 ++#%>
 
-
-<%= header_tags %>
-
 <div class="contextual">
 <%= link_to l(:label_export_card_configuration_new), {:action => 'new'}, :class => 'icon icon-add' %>
 </div>