ixgbe: Delete a bunch of dead code

All of the code involved with returning the supported physical
layer is actually unused, so delete it.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>