doc: simplify a C++ example

* doc/org/tut10.org: Remove a couple of useless includes.

doc/org/tut10.org

@@ -128,17 +128,14 @@ various preferences (like small or deterministic) or characteristic
 output as a never claim is done via the =print_never_claim= function.
 
 #+BEGIN_SRC C++ :results verbatim :exports both
-  #include <string>
   #include <iostream>
   #include <spot/tl/parse.hh>
-  #include <spot/tl/print.hh>
   #include <spot/twaalgos/translate.hh>
   #include <spot/twaalgos/neverclaim.hh>
 
   int main()
   {
-    std::string input = "[]<>p0 || <>[]p1";
-    spot::parsed_formula pf = spot::parse_infix_psl(input);
+    spot::parsed_formula pf = spot::parse_infix_psl("[]<>p0 || <>[]p1");
     if (pf.format_errors(std::cerr))
       return 1;
     spot::translator trans;