ELM includes a NotEqual node, but requires that it is shorthand for Not(Equal)

This has caused confusion for implementers, especially since there is no NotEquivalent node. In addition, the current CQL-to-ELM translator does not output NotEqual, it will always output Not(Equal), so there should be no actual usage of the node (at least in translated ELM, manually produced ELM may still have this issue).

Consider deprecating the NotEqual node to reduce confusion.

This will involve a deprecation note in the Logical specification, the translation semantics mapping, and a deprecation note in the ELM XML schema.