Remove duplicative call to get_page_count_for_letter

For some reason we were calling it twice. We can just reuse the
value already calculated

app/main/views/templates.py

@@ -77,7 +77,7 @@ def view_template(service_id, template_id):
                 filetype='png',
             ),
             show_recipient=True,
-            page_count=get_page_count_for_letter(template),
+            page_count=page_count,
         ),
         template_postage=template["postage"],
         user_has_template_permission=user_has_template_permission,