Remove heartbeat, relabel USB to JOC Midi

include/led_stub.h

@@ -35,8 +35,6 @@ private:
     bool initialized;
     uint32_t activity_off_time = 0;
     uint8_t saved_r = 0, saved_g = 0, saved_b = 0;
-    uint32_t heartbeat_time = 0;
-    uint8_t heartbeat_phase = 0;
     
 public:
     DefaultLedStub();