Remove NullOp::Box

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -680,7 +680,6 @@ impl Visitor<'tcx> for Checker<'mir, 'tcx> {
             }
 
             Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) => {}
-            Rvalue::NullaryOp(NullOp::Box, _) => self.check_op(ops::HeapAllocation),
             Rvalue::ShallowInitBox(_, _) => {}
 
             Rvalue::UnaryOp(_, ref operand) => {

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -517,7 +517,6 @@ impl<'tcx> Validator<'_, 'tcx> {
             }
 
             Rvalue::NullaryOp(op, _) => match op {
-                NullOp::Box => return Err(Unpromotable),
                 NullOp::SizeOf => {}
                 NullOp::AlignOf => {}
             },