Fixed missing typecast in duplicate_per_byte

Function `duplicate_per_byte` checks that the `init_expr` is at max
8-bit wide. However `shadow_memoryt::initialize_shadow_memory` was
removing the outer typecast to an 8-bit value, resulting in a call to
`duplicate_per_byte` with an `init_expr` larger than 8-bit.

This commit removes the typecast removal and fixes the issue.

Author: Enrico Steffinlongo

src/goto-symex/shadow_memory.cpp

@@ -50,8 +50,6 @@ void shadow_memoryt::initialize_shadow_memory(
     else
     {
       exprt init_expr = field_pair.second;
-      if(init_expr.id() == ID_typecast)
-        init_expr = to_typecast_expr(field_pair.second).op();
       const auto init_value =
         expr_initializer(type, expr.source_location(), ns, init_expr);
       CHECK_RETURN(init_value.has_value());