WFLY-3189 - Do not use schema location in schema element. 

Do not use schemaLocation when importing a namespace.

XML validators seem to get confused when schema location is specified
and imports / includes are circular. Instead rely on entries in XML
catalogue.

Related to https://github.com/wildfly/wildfly/pull/6720/
Related to https://github.com/jboss/metadata/pull/72
are we sure this is a good idea?
http://www.jboss.org/j2ee/schema/jboss-ejb3-spec-2_0.xsd seem to contain jboss specific elements not found in the normal java.sun.com/xml/ns/javaee xsd ?