Thread:

Postgres 9.6. We're attempting to delete some old users from a DB.

Log into DB as masteruser.

Run this block of commands (the_schema=public, and it's the only schema in this particular DB):

REVOKE ALL PRIVILEGES ON DATABASE the_database FROM old_role;
REVOKE USAGE ON SCHEMA the_schema FROM old_role;
REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA the_schema FROM old_role;
REVOKE ALL PRIVILEGES ON ALL SEQUENCES IN SCHEMA the_schema FROM old_role;

Here we actually had to create a loop to revoke one function at a time while avoiding system functions on which this single command fails:
REVOKE ALL PRIVILEGES ON ALL FUNCTIONS IN SCHEMA the_schema FROM old_role;

REVOKE ALL PRIVILEGES ON SCHEMA the_schema FROM old_role;
ALTER DEFAULT PRIVILEGES IN SCHEMA the_schema REVOKE ALL ON SEQUENCES FROM old_role;
ALTER DEFAULT PRIVILEGES IN SCHEMA the_schema REVOKE ALL ON TABLES FROM old_role;
ALTER DEFAULT PRIVILEGES IN SCHEMA the_schema REVOKE ALL ON FUNCTIONS FROM old_role;

REASSIGN OWNED BY old_role TO masteruser;
DROP OWNED BY old_role;
DROP USER old_role;                                                                                                                                    

The consensus online is that these are the steps to be taken to successfully remove roles, yet we get this error below:
                                 
ERROR:  role "old_role" cannot be dropped because some objects depend on it
DETAIL: privileges for database the_database 96 objects in database the_database SQL state: 2BP01