Remove duplicates of membership from results of \du

Hi, hackers

When executing \du, you can see duplicates of the same role in 'member of'.
This happens when admin | inherit | set options are granted by another role.

---
postgres=# create role role_a login createrole;
CREATE ROLE
postgres=# \du
                                   List of roles
 Role name | Attributes                         | Member of
-----------+------------------------------------------------------------+-----------
 role_a    | Create role                                               
| {}
 shinya    | Superuser, Create role, Create DB, Replication, Bypass RLS
| {}

postgres=# set role role_a;
SET
postgres=> create role role_b;
CREATE ROLE
postgres=> \du
                                   List of roles
 Role name | Attributes                         | Member of
-----------+------------------------------------------------------------+-----------
 role_a    | Create role                                               
| {role_b}
 role_b    | Cannot login                                              
| {}
 shinya    | Superuser, Create role, Create DB, Replication, Bypass RLS
| {}

postgres=> grant role_b to role_a;
GRANT ROLE
postgres=> \du
                                      List of roles
 Role name | Attributes                         |    Member of
-----------+------------------------------------------------------------+-----------------
 role_a    | Create role                                               
| {role_b,role_b}
 role_b    | Cannot login                                              
| {}
 shinya    | Superuser, Create role, Create DB, Replication, Bypass RLS
| {}

postgres=> select rolname, oid from pg_roles where rolname = 'role_b';
 rolname |  oid
---------+-------
 role_b  | 16401
(1 row)

postgres=> select * from pg_auth_members where roleid = 16401;
  oid  | roleid | member | grantor | admin_option | inherit_option |
set_option
-------+--------+--------+---------+--------------+----------------+------------
 16402 |  16401 |  16400 |      10 | t            | f | f
 16403 |  16401 |  16400 |   16400 | f            | t | t
(2 rows)
---

Attached patch resolves this issue.
Do you think?

Regards,
Shinya Kato