RC_Channel: remove the unused test function get_failsafe

libraries/RC_Channel/RC_Channel.cpp

@@ -197,13 +197,6 @@ RC_Channel::control_mix(float value)
     return (1 - abs(control_in / _high)) * value + control_in;
 }
 
-// are we below a threshold?
-bool
-RC_Channel::get_failsafe(void)
-{
-    return (radio_in < (radio_min - 50));
-}
-
 // returns just the PWM without the offset from radio_min
 void
 RC_Channel::calc_pwm(void)

libraries/RC_Channel/RC_Channel.h

@@ -78,9 +78,6 @@ public:
     // call after first set_pwm
     void        trim();
 
-    // did our read come in 50µs below the min?
-    bool        get_failsafe(void);
-
     // value generated from PWM
     int16_t         control_in;