You can drop custom roles but not default roles.
Drop a role by using an SQL statement
You can use the DROP ROLE statement to drop a role that you no longer need. To drop a role, you must have the DROP ANY ROLE privilege and are granted the WITH ADMIN OPTION privilege of the role to be dropped.
For information about how to view your privileges, see View user privileges. If you do not have the required privilege, contact an administrator. For more information, see Modify user privileges.
When you drop a role, the system revokes the role from all users and roles and then deletes the role from the database.
Notice
Dropping a role does not affect user sessions in which the role is enabled. However, after the role is dropped, the role can no longer be enabled in new user sessions.
Syntax for the SQL statement:
obclient> DROP ROLE role_name;
Examples:
obclient> DROP ROLE role1;
Query OK, 0 rows affected
For more information about the DROP ROLE statement, see DROP ROLE.