Don't try to constant-fold functions returning RECORD. We were never

Don't try to constant-fold functions returning RECORD.  We were never
able to do this before, but I had tried to make an exception for functions
with OUT parameters.  Michael Fuhr found one problem with it already, and
I found another, which was it didn't work for strict functions with a
NULL input.  While both of these could be worked around, the probability
that there are more gotchas seems high; I think prudence dictates just
reverting to the former behavior for now.  Accordingly, remove the kluge
added to get_expr_result_type() for Michael's case.