don't include token in dashboard link, when available (#1406)

Author: minrk

jupyter_server/templates/page.html

@@ -34,8 +34,7 @@
 
   <div id="header" role="navigation" aria-label="{% trans %}Top Menu{% endtrans %}">
     <div id="header-container" class="container">
-      <div id="jupyter_server" class="nav navbar-brand"><a href="{{default_url}}
-    {%- if logged_in and token -%}?token={{token}}{%- endif -%}" title='{% trans %}dashboard{% endtrans %}'>
+      <div id="jupyter_server" class="nav navbar-brand"><a href="{{default_url}}" title='{% trans %}dashboard{% endtrans %}'>
           {% block logo %}<img src='{{static_url("logo/logo.png") }}' alt='Jupyter Server' />{% endblock %}
         </a></div>