i40e: Remove string printing for i40e_status

Remove the i40e_stat_str() function which prints the string
representation of the i40e_status error code. With upcoming changes
moving away from i40e_status, there will be no need for this function

Signed-off-by: Jan Sokolowski <jan.sokolowski@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>