Patch to fix documentation about AFTER triggers

Here is a patch to amend the docs here:

https://www.postgresql.org/docs/devel/static/plpgsql-trigger.html

In the example for an AFTER trigger, you see this code:

--
-- Create a row in emp_audit to reflect the operation performed on emp,
-- make use of the special variable TG_OP to work out the operation.
--
IF (TG_OP = 'DELETE') THEN
INSERT INTO emp_audit SELECT 'D', now(), user, OLD.*;
RETURN OLD;
ELSIF (TG_OP = 'UPDATE') THEN
INSERT INTO emp_audit SELECT 'U', now(), user, NEW.*;
RETURN NEW;
ELSIF (TG_OP = 'INSERT') THEN
INSERT INTO emp_audit SELECT 'I', now(), user, NEW.*;
RETURN NEW;
END IF;
RETURN NULL; -- result is ignored since this is an AFTER trigger

What are all those RETURNs doing in there? The comment on the final
RETURN is correct, so returning NEW or OLD above seems confusing, and
likely a copy/paste error.

This patch just removes those three lines from the example code.

Thanks!
Paul