Element mistakenly removed from beans_2_0.xsd

While creating and editing beans_2_0.xsd there was one line removed as part of this PR. This line is present in beans_1_1.xsd -> see the code.

To sum up the meaning of this line, it allows presence of any other non-defined element from other namespace (than target namespace) and further on enforces validation of such element against corresponding XSD.

As a consequence of this change, following beans.xml is valid with CDI 1.2 (beans_1_1.xsd) but no longer against CDI 2.0 (beans_2_0.xsd):

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:weld="http://jboss.org/schema/weld/beans"
       xmlns="http://xmlns.jcp.org/xml/ns/javaee"
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
        http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
       bean-discovery-mode="all">
    <weld:scan>
        <weld:include name="my.package.*"/>
    </weld:scan>
</beans>