remove "start" duplicity in setup

Firmware/Marlin_main.cpp

@@ -1181,7 +1181,6 @@ void setup()
 	MYSERIAL.begin(BAUDRATE);
 	fdev_setup_stream(uartout, uart_putchar, NULL, _FDEV_SETUP_WRITE); //setup uart out stream
 	stdout = uartout;
-	SERIAL_PROTOCOLLNPGM("start");
 	SERIAL_ECHO_START;
 	printf_P(PSTR(" " FW_VERSION_FULL "\n"));