AP_Arming: use functor macros

Functor is not yet being used but let's make is macro fallback to the
previous Delegate implementation for easy of transition between the two.

libraries/AP_Arming/AP_Arming.h

@@ -37,8 +37,8 @@ public:
         YES_ZERO_PWM = 2
     };
 
-    //for the hacky funciton pointer to gcs_send_text_p
-    typedef DELEGATE_FUNCTION2(void, gcs_severity, const prog_char_t*) gcs_send_t_p;
+    // for the hacky function pointer to gcs_send_text_p
+    FUNCTOR_TYPEDEF(gcs_send_t_p, void, gcs_severity, const prog_char_t *);
 
     AP_Arming(const AP_AHRS &ahrs_ref, const AP_Baro &baro, Compass &compass,
               const enum HomeState &home_set, gcs_send_t_p);