All you need 2 do is when you open a new package select create package info
in the package info add the following annotation or change it as needed
@javax.xml.bind.annotation.XmlSchema(namespace = "http://www.sitemaps.org/schemas/sitemap/0.9", elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED, xmlns = { @javax.xml.bind.annotation.XmlNs(namespaceURI = "http://www.sitemaps.org/schemas/sitemap/0.9", prefix = "") })
This will remove the ns2 prefix