[Black_F407] Clean some comments

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

variants/BLACK_F407XX/variant.h

@@ -290,15 +290,9 @@ extern "C" {
 
 // UART Definitions
 // Define here Serial instance number to map on Serial generic name
-#define SERIAL_UART_INSTANCE    1 //ex: 2 for Serial2 (USART2)
-// DEBUG_UART could be redefined to print on another instance than 'Serial'
-//#define DEBUG_UART              ((USART_TypeDef *) U(S)ARTX) // ex: USART3
-// DEBUG_UART baudrate, default: 9600 if not defined
-//#define DEBUG_UART_BAUDRATE     x
-// DEBUG_UART Tx pin name, default: the first one found in PinMap_UART_TX for DEBUG_UART
-//#define DEBUG_PINNAME_TX        PX_n // PinName used for TX
+#define SERIAL_UART_INSTANCE    1
 
-// Default pin used for 'Serial' instance (ex: ST-Link)
+// Default pin used for 'Serial' instance
 // Mandatory for Firmata
 #define PIN_SERIAL_RX           PA10
 #define PIN_SERIAL_TX           PA9