Fix a RelaxNG violation

A mistake was made during a sync with doc-en, these example tags do not exist

Author: Girgias

reference/mysqli/mysqli_stmt/prepare.xml

@@ -143,8 +143,6 @@ $stmt->fetch();
 printf("%s is in district %s\n", $city, $district);
 ]]>
    </programlisting>
-  </example>
-  <example>
    <para>&style.procedural;</para>
    <programlisting role="php">
 <![CDATA[