i40e: remove Tx work for ptp

The previous removal of the PTP Tx work functionality was
incomplete as noted by Jake Keller. This removal allows
us to rely on the Tx timesync interrupt.

CC: Jacob Keller <jacob.e.keller@intel.com>
Change-ID: Id4faaf275a3688053ebbf07bef08072f9fd11aa9
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>