RC_Channel: remove unused control_mix method

libraries/RC_Channel/RC_Channel.cpp

@@ -221,12 +221,6 @@ RC_Channel::set_pwm_no_deadzone(int16_t pwm)
     }
 }
 
-int16_t
-RC_Channel::control_mix(float value)
-{
-    return (1 - abs(control_in / _high_in)) * value + control_in;
-}
-
 // returns just the PWM without the offset from radio_min
 void
 RC_Channel::calc_pwm(void)

libraries/RC_Channel/RC_Channel.h

@@ -85,8 +85,6 @@ public:
     // value generated from PWM
     int16_t         control_in;
 
-    int16_t         control_mix(float value);
-
     // current values to the servos - degrees * 100 (approx assuming servo is -45 to 45 degrees except [3] is 0 to 100
     int16_t        servo_out;