Remove debug output for USART example.

example-usb-serial/README

@@ -2,3 +2,8 @@ This is an application example using ST Nucleo F103 board.
 
 SB62 and SB63 should be soldered.
 ST-Link/V2 is disconnected (SB13 and SB14).
+
+TODO:
+* serial config setting
+* stats report control
+* Use of DMA for serial communication

example-usb-serial/sample.c

@@ -114,8 +114,6 @@ cdc_to_usart_loop (void *arg)
 
 	  if (size)
 	    usart_write (cdc_usart->dev_no, s, size);
-	  else
-	    usart_write (cdc_usart->dev_no, "HELLO!\r\n", 8);
 	}
     }