ibmvnic: Remove unused TSO resources in TX pool structure

Finally, remove the TSO-specific fields in the TX pool
strcutures. These are no longer needed with the introduction
of separate buffer pools for TSO transmissions.

Signed-off-by: Thomas Falcon <tlfalcon@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>