## WorkWrap should eliminate unlifted absent coercions

From #18982 (closed):

```
{-# LANGUAGE GADTs #-}
module Lib where
data GADT a where
GADT :: Int -> GADT Int
h :: GADT a -> Int
h (GADT n) = n
{-# NOINLINE h #-}
```

produces

```
Lib.$wh [InlPrag=NOINLINE]
:: forall a. (a GHC.Prim.~# Int) -> GHC.Prim.Int# -> GHC.Prim.Int#
Lib.$wh
= \ (@ a_sxO)
(ww_sxS [Dmd=<L,A>] :: a_sxO GHC.Prim.~# Int)
(ww1_sxW :: GHC.Prim.Int#) ->
ww1_sxW
-- RHS size: {terms: 14, types: 18, coercions: 1, joins: 0/0}
h [InlPrag=NOUSERINLINE[0]] :: forall a. GADT a -> Int
h = \ (@ a_sxO) (w_sxP :: GADT a_sxO) ->
case w_sxP of { GADT ww1_sxS [Dmd=<L,A>] ww2_sxT ->
case ww2_sxT of { GHC.Types.I# ww4_sxW ->
case Lib.$wh @ a_sxO @~ (ww1_sxS :: a_sxO GHC.Prim.~# Int) ww4_sxW
of ww5_sy1
{ __DEFAULT ->
GHC.Types.I# ww5_sy1
}
}
}
```

The coercion argument to the worker `$wh`

is absent, but still present in the simplified code. It would be good if we can change that, as it also makes the type argument `@a`

dead. Then we end up with a much simpler worker and call site.

Not that it would impact runtime performance other than maybe through inlining decisions.

I think the problem has to do with "what kind of absent dummy should we pick for the coercion type?".