i40e: don't disable PF LB when disabling VFs

Since we now have functionality to enable and disable PF loopback at
runtime, don't try to do it automatically. Removing this call also gets
rid of a bogus error message when removing the PF module with VFs
enabled.

Change-ID: Ic38652d8a3b9498d96113bfaa5ea7bad050862e9
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>