[XQuery] IBM-XQ-004: Remove namespace nodes from XQuery document

(IBM-XQ-004) In the XQuery document, there should be no reference to 
"namespace nodes". Since XQuery does not support the namespace axis, there 
is no way for an expression to return a namespace node. All references to 
namespace nodes should be replaced by references to the "in-scope 
namespaces" of an element, a term that is already widely used in both the 
Data Model and the Functions and Operators documents. Nodes are needed 
only to preserve identity and to represent a position on an axis. Since 
namespace-prefix-bindings in XQuery have neither identity nor position, 
there is no need in XQuery for the concept of a "namespace node". See 
IBM-DM-031 for a related Data Model comment, but note that this proposal 
can be adopted independently of IBM-DM-031 (
https://lists.w3.org/Archives/Public/public-qt-comments/2004Feb/0207.html)
--Don Chamberlin