Remove unsupported 'updated' flag from _includes/post/date.html

Jekyll does not support this value for Page or Post classes. The
capture returned an empty Sting, which was always evaluated to true
in '{% if updated %}'.

.themes/classic/source/_layouts/page.html

@@ -15,7 +15,7 @@ layout: default
     <footer>
       {% if page.date or page.author %}<p class="meta">
         {% if page.author %}{% include post/author.html %}{% endif %}
-        {% include post/date.html %}{% if updated %}{{ updated }}{% else %}{{ time }}{% endif %}
+        {% include post/date.html %}{{ time }}
         {% if page.categories %}{% include post/categories.html %}{% endif %}
       </p>{% endif %}
       {% unless page.sharing == false %}