bitbake: toaster: don't use mru.count in the template

mru is a list. It has a count method, but it differs from the
one for the queryset. Using mru.count causes 'Latest project builds'
section to silently disappear when toaster runs on python 3.

(Bitbake rev: c3ff90c9f028bff5733ebac7b5e72a4688addd3e)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/toaster/toastergui/templates/mrb_section.html

@@ -18,7 +18,7 @@
   });
 </script>
 
-{%if mru and mru.count > 0%}
+{%if mru %}
 
   {%if mrb_type == 'project' %}
       <h2 class="page-header">