Remove redundant API in smtk::attribute::Attribute
API that seems to do nearly the same things:
associatedObjects(), associations(), associatedModelEntityIds(), associatedModelEntities()
associate(smtk::resource::PersistentObjectPtr obj), associateEntity(const smtk::common::UUID& entity), associateEntity(const smtk::model::EntityRef& entity)
disassociateEntity(const smtk::common::UUID& entity, bool reverse = true), disassociateEntity(const smtk::model::EntityRef& entity, bool reverse = true), disassociate(smtk::resource::PersistentObjectPtr obj, bool reverse = true);
isObjectAssociated(const smtk::resource::PersistentObjectPtr& componentPtr), isEntityAssociated(const smtk::model::EntityRef& entityref)