Cleanup yang-parser-spi namespaces

yang-parser-spi namespaces do not correctly capture statement relationships – for example IdentityNamespace is defined as:

StatementNamespace<QName, IdentityStatement, EffectiveStatement<QName, IdentityStatement>>

whereas it should be defined as:

StatementNamespace<QName, IdentityStatement, IdentityEffectiveStatement>

Correct this mistake, which comes from the fact the effective statement interfaces were not defined until just before the 2.0.0 release