requires_renaming must not recurse into array subtypes in structs

Just like pointers, array members may have subtypes of the same type as the
containing struct. The behaviour/check now matches what the actual renaming
function uses.

Also clean up the unnecessary ID_class, which does not actually exist.

Author: tautschnig

regression/cbmc/struct12/main.c

@@ -0,0 +1,12 @@
+struct S
+{
+  struct S *s;
+  struct S *a[2];
+};
+
+int main()
+{
+  struct S s;
+  s.s = 0;
+  return 0;
+}

regression/cbmc/struct12/test.desc

@@ -0,0 +1,8 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+^VERIFICATION SUCCESSFUL$
+--
+^warning: ignoring

src/goto-symex/goto_symex_state.cpp

@@ -622,16 +622,20 @@ static bool requires_renaming(const typet &type, const namespacet &ns)
     return requires_renaming(array_type.subtype(), ns) ||
            !array_type.size().is_constant();
   }
-  else if(
-    type.id() == ID_struct || type.id() == ID_union || type.id() == ID_class)
+  else if(type.id() == ID_struct || type.id() == ID_union)
   {
     const struct_union_typet &s_u_type = to_struct_union_type(type);
     const struct_union_typet::componentst &components = s_u_type.components();
 
     for(auto &component : components)
     {
       // be careful, or it might get cyclic
-      if(
+      if(component.type().id() == ID_array)
+      {
+        if(!to_array_type(component.type()).size().is_constant())
+          return true;
+      }
+      else if(
         component.type().id() != ID_pointer &&
         requires_renaming(component.type(), ns))
       {