presto-main/src/main/java/io/prestosql/metadata/MetadataManager.java/MetadataManager/dropRole
class MetadataManager:    @Override
    public void dropRole(Session session, String role, String catalog)
    {
        CatalogMetadata catalogMetadata = getCatalogMetadataForWrite(session, catalog);
        CatalogName catalogName = catalogMetadata.getCatalogName();
        ConnectorMetadata metadata = catalogMetadata.getMetadata();

        metadata.dropRole(session.toConnectorSession(catalogName), role);
    }