Replace use of get_l1_object by remove_level_2

get_l1_object suggests we are comparing the address of the object, but
the actually should interpret the symbol itself as a pointer.
A unit test for the case of the issue that is fixed will be added in a
following commit.

Author: romainbrenguier

src/goto-symex/symex_goto.cpp

@@ -100,8 +100,10 @@ static optionalt<renamedt<exprt, L2>> try_evaluate_pointer_comparison(
   const ssa_exprt *ssa_symbol_expr =
     expr_try_dynamic_cast<ssa_exprt>(symbol_expr);
 
+  ssa_exprt l1_expr{*ssa_symbol_expr};
+  l1_expr.remove_level_2();
   const std::vector<exprt> value_set_elements =
-    value_set.get_value_set(ssa_symbol_expr->get_l1_object(), ns);
+    value_set.get_value_set(l1_expr, ns);
 
   bool constant_found = false;