Use not-as-deprecated version of to_integer

Author: tautschnig

src/util/arith_tools.h

@@ -10,14 +10,13 @@ Author: Daniel Kroening, [email protected]
 #ifndef CPROVER_UTIL_ARITH_TOOLS_H
 #define CPROVER_UTIL_ARITH_TOOLS_H
 
+#include "invariant.h"
 #include "mp_arith.h"
 #include "optional.h"
-#include "invariant.h"
+#include "std_expr.h"
 
 #include "deprecate.h"
 
-class exprt;
-class constant_exprt;
 class typet;
 
 // this one will go away
@@ -49,7 +48,7 @@ struct numeric_castt<mp_integer> final
   optionalt<mp_integer> operator()(const exprt &expr) const
   {
     mp_integer out;
-    if(to_integer(expr, out))
+    if(expr.id() != ID_constant || to_integer(to_constant_expr(expr), out))
       return {};
     return out;
   }