Rover: remove unused throttle_failsafe_active method

APMrover2/Rover.h

@@ -510,7 +510,6 @@ private:
     void rudder_arm_disarm_check();
     void read_radio();
     void control_failsafe(uint16_t pwm);
-    bool throttle_failsafe_active();
     void trim_control_surfaces();
     void trim_radio();
 

APMrover2/radio.cpp

@@ -175,25 +175,6 @@ void Rover::control_failsafe(uint16_t pwm)
     }
 }
 
-/*
-  return true if throttle level is below throttle failsafe threshold
-  or RC input is invalid
- */
-bool Rover::throttle_failsafe_active(void)
-{
-    if (!g.fs_throttle_enabled) {
-        return false;
-    }
-    if (millis() - failsafe.last_valid_rc_ms > 1000) {
-        // we haven't had a valid RC frame for 1 seconds
-        return true;
-    }
-    if (channel_throttle->get_reverse()) {
-        return channel_throttle->get_radio_in() >= g.fs_throttle_value;
-    }
-    return channel_throttle->get_radio_in() <= g.fs_throttle_value;
-}
-
 void Rover::trim_control_surfaces()
 {
     read_radio();