Update main_statements.md

Author: flexferrum

docs/usage/main_statements.md

@@ -80,9 +80,6 @@ I.e. left part of this expression (before 'if') is a true-branch of the statemen
     forloop.prev = {{ forloop.prev }}</br>
     forloop.next = {{ forloop.prev }}</br>
     forloop.index = {{ forloop.prev }}</br>
-    {% if not forloop.first %}
-    prev_url = {{ children_list[forloop.index0 - 1].url }}</br>
-    {% endif %}
     <a href="{{ child.url | absolute_url }}">{{ child.title }}</a>
   {% endif %}
 {% endfor %}