OPENDJ-3089 Fix calls to server Schema methods that are not available in SDK Schema

- replace calls to "schema.getSchemaNG()" by "schema" as schema is now the
SDK schema
- replace calls to "schema.updateSchemaOption()" by
"schemaHandler.updateSchemaOption()"
- replace calls to "schema.parseX()" by "SchemaUtils.parseXOID()" where X =
schema element
- replace calls to "schema.registerX()" and "schema.deregisterX()" where X =
schema element by calls to "schemaHandler.updateSchema()"