CPR analysis worker returns values the wrapper could trivially construct itself

Consider GHC.Num.Natural.naturalNegate:

naturalNegate :: Natural -> Natural
{-# NOINLINE naturalNegate #-}
naturalNegate (NS 0##) = NS 0##
naturalNegate _        = raiseUnderflow

This will create the following WW split:

naturalNegate n = case $wnaturalNegate n of b -> NS b

$wnaturalNegate :: Natural -> Word#
{-# NOINLINE $wnaturalNegate #-}
$wnaturalNegate (NS 0##) = 0##
$wnaturalNegate _        = case raiseUnderflow of {}

but that 0## is an expression that is both cheap to evaluate and not free in any of the parameters of the function. We could just as well construct it in the wrapper:

naturalNegate n = case $wnaturalNegate n of () -> NS 0##

$wnaturalNegate :: Natural -> ()
{-# NOINLINE $wnaturalNegate #-}
$wnaturalNegate (NS 0##) = ()
$wnaturalNegate _        = case raiseUnderflow of {}

This transformation would be completely within reach for Nested CPR; the only question is whether we want it. Maybe we should only do this for literal expressions for code size concerns.