chore(cdc): drop the unused USBD_CDC_ClearBuffer

USBD_CDC_Receive() was its only caller. The helper is not part of the
ST USB device middleware, it is local to this core, and the only thing
it does is arm the OUT endpoint with a NULL application buffer, which
is what made a receive overrun fault the MCU.

Remove it so it cannot be reused. This also drops a USE_USBD_COMPOSITE
branch that would not compile: it reads a bare classId instead of
pdev->classId.

Author: dldntjr407

libraries/USBDevice/inc/usbd_cdc.h

@@ -148,12 +148,10 @@ uint8_t USBD_CDC_RegisterInterface(USBD_HandleTypeDef *pdev,
 uint8_t USBD_CDC_SetTxBuffer(USBD_HandleTypeDef *pdev, uint8_t *pbuff,
                              uint32_t length, uint8_t ClassId);
 uint8_t USBD_CDC_TransmitPacket(USBD_HandleTypeDef *pdev, uint8_t ClassId);
-uint8_t USBD_CDC_ClearBuffer(USBD_HandleTypeDef *pdev, uint8_t ClassId);
 #else
 uint8_t USBD_CDC_SetTxBuffer(USBD_HandleTypeDef *pdev, uint8_t *pbuff,
                              uint32_t length);
 uint8_t USBD_CDC_TransmitPacket(USBD_HandleTypeDef *pdev);
-uint8_t USBD_CDC_ClearBuffer(USBD_HandleTypeDef *pdev);
 #endif /* USE_USBD_COMPOSITE */
 uint8_t USBD_CDC_SetRxBuffer(USBD_HandleTypeDef *pdev, uint8_t *pbuff);
 uint8_t USBD_CDC_ReceivePacket(USBD_HandleTypeDef *pdev);

libraries/USBDevice/src/cdc/usbd_cdc.c

@@ -1019,24 +1019,6 @@ uint8_t USBD_CDC_ReceivePacket(USBD_HandleTypeDef *pdev)
 
   return (uint8_t)USBD_OK;
 }
-#ifdef USE_USBD_COMPOSITE
-uint8_t USBD_CDC_ClearBuffer(USBD_HandleTypeDef *pdev, uint8_t ClassId)
-{
-  /* Suspend or Resume USB Out process */
-  if (pdev->pClassDataCmsit[classId] != NULL) {
-#else
-uint8_t USBD_CDC_ClearBuffer(USBD_HandleTypeDef *pdev)
-{
-  /* Suspend or Resume USB Out process */
-  if (pdev->pClassDataCmsit[pdev->classId] != NULL) {
-#endif /* USE_USBD_COMPOSITE */
-    /* Prepare Out endpoint to receive next packet */
-    USBD_LL_PrepareReceive(pdev, CDC_OUT_EP, 0, 0);
-    return (uint8_t)USBD_OK;
-  } else {
-    return (uint8_t)USBD_FAIL;
-  }
-}
 
 #endif /* USBD_USE_CDC */
 #endif /* USBCON */