Remove obsolete code in CoreToStg

Note [Nullary unboxed tuple] was removed in e9e61f18.
This codepath is tested by T15696_3.

compiler/GHC/CoreToStg.hs

@@ -49,7 +49,6 @@ import GHC.Types.Demand    ( isUsedOnceDmd )
 import GHC.Types.SrcLoc    ( mkGeneralSrcSpan )
 
 import GHC.Unit.Module
-import GHC.Builtin.Types ( unboxedUnitDataCon )
 import GHC.Data.FastString
 import GHC.Platform.Ways
 import GHC.Builtin.PrimOps ( PrimCall(..) )
@@ -462,15 +461,6 @@ coreToStgExpr (Case scrut bndr _ alts)
   where
     vars_alt :: CoreAlt -> CtsM StgAlt
     vars_alt (Alt con binders rhs)
-      | DataAlt c <- con, c == unboxedUnitDataCon
-      = -- This case is a bit smelly.
-        -- See Note [Nullary unboxed tuple] in GHC.Core.Type
-        -- where a nullary tuple is mapped to (State# World#)
-        assert (null binders) $
-        do { rhs2 <- coreToStgExpr rhs
-           ; return GenStgAlt{alt_con=DEFAULT,alt_bndrs=mempty,alt_rhs=rhs2}
-           }
-      | otherwise
       = let     -- Remove type variables
             binders' = filterStgBinders binders
         in

testsuite/tests/linters/notes.stdout

@@ -22,7 +22,6 @@ ref    compiler/GHC/Core/Unfold.hs:1242:50:     Note [Unfold info lazy contexts]
 ref    compiler/GHC/Core/Unfold/Make.hs:157:34:     Note [DFunUnfoldings]
 ref    compiler/GHC/Core/Unify.hs:1390:9:     Note [INLINE pragmas and (>>)]
 ref    compiler/GHC/Core/Utils.hs:947:40:     Note [ _       -> [con1]
-ref    compiler/GHC/CoreToStg.hs:462:15:     Note [Nullary unboxed tuple]
 ref    compiler/GHC/Driver/Main.hs:1566:34:     Note [simpleTidyPgm - mkBootModDetailsTc]
 ref    compiler/GHC/Driver/Session.hs:1947:36:     Note [GHC.Driver.Main . Safe Haskell Inference]
 ref    compiler/GHC/Driver/Session.hs:3916:49:     Note [Eta-reduction in -O0]