Rover: remove usb-mux checking

Nobody ever uses the result from this

APMrover2/APMrover2.cpp

@@ -66,7 +66,6 @@ const AP_Scheduler::Task Rover::scheduler_tasks[] = {
     SCHED_TASK(read_aux_switch,        10,    200),
     SCHED_TASK_CLASS(AP_BattMonitor,      &rover.battery,          read,           10,  300),
     SCHED_TASK_CLASS(AP_ServoRelayEvents, &rover.ServoRelayEvents, update_events,  50,  200),
-    SCHED_TASK(check_usb_mux,           3,    200),
 #if MOUNT == ENABLED
     SCHED_TASK_CLASS(AP_Mount,            &rover.camera_mount,     update,         50,  200),
 #endif

APMrover2/GCS_Mavlink.cpp

@@ -1222,7 +1222,6 @@ void Rover::mavlink_delay_cb()
         last_5s = tnow;
         gcs().send_text(MAV_SEVERITY_INFO, "Initialising APM");
     }
-    check_usb_mux();
 
     DataFlash.EnableWrites(true);
 }

APMrover2/Rover.h

@@ -231,9 +231,6 @@ private:
     // true if initialisation has completed
     bool initialised;
 
-    // if USB is connected
-    bool usb_connected;
-
     // This is the state of the flight control system
     // There are multiple states defined such as MANUAL, AUTO, ...
     Mode *control_mode;
@@ -525,7 +522,6 @@ private:
     bool set_mode(Mode &new_mode, mode_reason_t reason);
     bool mavlink_set_mode(uint8_t mode);
     void startup_INS_ground(void);
-    void check_usb_mux(void);
     void print_mode(AP_HAL::BetterStream *port, uint8_t mode);
     void notify_mode(const Mode *new_mode);
     uint8_t check_digital_pin(uint8_t pin);

APMrover2/system.cpp

@@ -70,11 +70,6 @@ void Rover::init_ardupilot()
     // init baro before we start the GCS, so that the CLI baro test works
     barometer.init();
 
-    // we start by assuming USB connected, as we initialed the serial
-    // port with SERIAL0_BAUD. check_usb_mux() fixes this if need be.
-    usb_connected = true;
-    check_usb_mux();
-
     // setup telem slots with serial ports
     gcs().setup_uarts(serial_manager);
 
@@ -288,17 +283,6 @@ void Rover::startup_INS_ground(void)
     ahrs.reset();
 }
 
-void Rover::check_usb_mux(void)
-{
-    bool usb_check = hal.gpio->usb_connected();
-    if (usb_check == usb_connected) {
-        return;
-    }
-
-    // the user has switched to/from the telemetry port
-    usb_connected = usb_check;
-}
-
 // update notify with mode change
 void Rover::notify_mode(const Mode *mode)
 {