can: usb_8dev: remove unused member echo_skb from struct usb_8dev_priv

This patch removes the unused memberecho_skb from the struct
usb_8dev_priv.

Fixes: 0024d8ad ("can: usb_8dev: Add support for USB2CAN interface from 8 devices")
Link: https://lore.kernel.org/all/20220104230753.956520-1-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/usb_8dev.c

@@ -121,8 +121,6 @@ struct usb_8dev_tx_urb_context {
 struct usb_8dev_priv {
 	struct can_priv can; /* must be the first member */
 
-	struct sk_buff *echo_skb[MAX_TX_URBS];
-
 	struct usb_device *udev;
 	struct net_device *netdev;