Deleting duplicate rows using ctid ?

[David Gauthier]

I have a table with 4 columns, none of them unique.  I want to delete all
but one of the duplicate records.  I think there's a way to do this with
ctid.  Examples that pop up in google searches always rely on something
like a unique (id) field, like a primary key,  (no good in my case)

create table dog (variety varchar, name varchar, color varchar, age int);
insert into dogs
  ('lab','moby','white',12),
  ('lab','moby','white',12),
  ('spaniel','max','black',13),
  ('spaniel','max','black'),13,
  ('lab','moby','white',12);

I want the result to be just 2 recs, one for each dog.