HAL_ChibiOS: don't init serial 1 and 3

these should not be treated as special. Initialising them early just
wastes memory if the end up not being used

libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp

@@ -202,8 +202,6 @@ static void main_loop()
     ChibiOS::SPIDevice::test_clock_freq();
 #endif
 
-    hal.serial(3)->begin(38400);
-    hal.serial(1)->begin(57600);
     hal.analogin->init();
     hal.scheduler->init();