Find objects linked to a PostgreSQL role
Answer to question asked

To look for the function in the error message and its owner:

SELECT oid::regprocedure AS function
     , pg_get_userbyid(proowner) AS owner
FROM   pg_proc
WHERE  oid = 'text(boolean)'::regprocedure;


Related:


DROP FUNCTION without knowing the number/type of parameters?


Actual problem

The error message says:


  DETAIL:  privileges for function text(boolean)


It's not about ownership but about privileges.

The manual for DROP ROLE:


  Before dropping the role, you must drop all the objects it owns (or
  reassign their ownership) and revoke any privileges the role has been
  granted on other objects.


And for ALTER DEFAULT PRIVILEGES:


  If you wish to drop a role for which the default privileges have been
  altered, it is necessary to reverse the changes in its default
  privileges or use DROP OWNED BY to get rid of the default privileges
  entry for the role.


It also looks like you only executed REASSIGN OWNED in one DB, but the manual instructs: 


  Because REASSIGN OWNED does not affect objects within other
  databases, it is usually necessary to execute this command in each
  database that contains objects owned by a role that is to be removed.


Bold emphasis mine.

And you restricted your commands with IN SCHEMA public. Drop that clause to target the whole DB. But don't bother, there is a ...

Simple solution with DROP OWNED

REASSIGN OWNED BY user1 TO postgres;
DROP OWNED BY user1;


All the role's objects changed ownership to postgres with the first command and are safe now. The wording of DROP OWNED is a bit misleading, since it also gets rid of all privileges and default privileges. The manual for DROP OWNED:


  DROP OWNED drops all the objects within the current database that are
  owned by one of the specified roles. Any privileges granted to the
  given roles on objects in the current database and on shared objects
  (databases, tablespaces) will also be revoked.


Repeat in all relevant DBs, then you can move in for the kill:

DROP ROLE user1;