presto-hive/src/main/java/io/prestosql/plugin/hive/metastore/file/FileHiveMetastore.java/FileHiveMetastore/dropRole
class FileHiveMetastore:    @Override
    public synchronized void dropRole(String role)
    {
        Set<String> roles = new HashSet<>(listRoles());
        roles.remove(role);
        writeFile("roles", getRolesFile(), rolesCodec, ImmutableList.copyOf(roles), true);
        Set<RoleGrant> grants = listRoleGrantsSanitized();
        writeRoleGrantsFile(grants);
    }