Deprecate 7.2.4 Requirements class: Schematron extends XML schema

[cnreediii]

Should the schematron requirements calls be moved to an annex? And should this requirements class be deprecated? This may need dialogue with the entire TC (ask the question) as well as OSGeo and Shapechange communities.

[cnreediii]

Latest discussion is to merge Schematron section into XML section.

[cmheazel]

Schematron is a rules engine for validating the contents of an XML document. These rules require prior-knowledge of the structure of the document. Therefore, an XML document must first pass schema validation before you can apply the Schematron rules. XML Schema and Schematron are two phases of the same validation process.

[cnreediii]

Consensus initial decision is to merge Schematron requirements into XML model section.