i40e: drop unused debugfs file "dump"

There was a completely unused file "dump" in debugfs that
never panned out to be useful.

Change-ID: I12bb9e37b5a83299725dda815a8746157baf6562
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>