Remove unnecessary check on set-returning functions in values_lists

Hi,

I would like to understand the pull_up_simple_values code a little bit more.
Pull-up of simple values was implemented in 2015 by commit f4abd02. In
the is_simple_values I see a check on the expression_returns_set() of
the RTE values list.

But since d43a619 in 2017 the check_srf_call_placement has reported an
ERROR in the case of set-returning function inside a VALUES expression.
Let's demonstrate:

SELECT * FROM (VALUES ((generate_series(1,1E2))));
ERROR: set-returning functions are not allowed in VALUES
LINE 1: SELECT * FROM (VALUES ((generate_series(1,1E2))));

I think, the expression_returns_set examination doesn't necessary and we
can replace it with an assertion, if needed (see attachment).
Am I wrong?

--
regards, Andrei Lepikhov