With commit b56fc3c5 ("hv_netvsc: Fix a bug in netvsc_start_xmit()"),
skb variable is no longer used in netvsc_send. Remove variable and dead
code that depended on it.

Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NJerry Snitselaar <jsnitsel@redhat.com>
Signed-off-by: NHaiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>