GCS_MAVLink: use singleton to get AP_AdvancedFailsafe pointer

libraries/GCS_MAVLink/GCS.h

@@ -282,7 +282,6 @@ protected:
     // overridable method to check for packet acceptance. Allows for
     // enforcement of GCS sysid
     bool accept_packet(const mavlink_status_t &status, const mavlink_message_t &msg);
-    virtual AP_AdvancedFailsafe *get_advanced_failsafe() const { return nullptr; };
     virtual bool set_mode(uint8_t mode) = 0;
     void set_ekf_origin(const Location& loc);
 

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -2490,7 +2490,7 @@ MAV_RESULT GCS_MAVLINK::handle_preflight_reboot(const mavlink_command_long_t &pa
  */
 MAV_RESULT GCS_MAVLINK::handle_flight_termination(const mavlink_command_long_t &packet)
 {
-    AP_AdvancedFailsafe *failsafe = get_advanced_failsafe();
+    AP_AdvancedFailsafe *failsafe = AP::advancedfailsafe();
     if (failsafe == nullptr) {
         return MAV_RESULT_UNSUPPORTED;
     }
@@ -4631,7 +4631,7 @@ uint64_t GCS_MAVLINK::capabilities() const
         ret |= MAV_PROTOCOL_CAPABILITY_MAVLINK2;
     }
 
-    AP_AdvancedFailsafe *failsafe = get_advanced_failsafe();
+    AP_AdvancedFailsafe *failsafe = AP::advancedfailsafe();
     if (failsafe != nullptr && failsafe->enabled()) {
         // Copter and Sub may also set this bit as they can always terminate
         ret |= MAV_PROTOCOL_CAPABILITY_FLIGHT_TERMINATION;