ixgbe: remove unneeded ipsec state free callback

With commit 7f05b467 ("xfrm: check for xdo_dev_state_free")
we no longer need to add an empty callback function
to the driver, so now let's remove the useless code.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>