i40e: Remove EMPR traces from debugfs facility

Since commit
'5098850c ("i40e/i40evf: i40e_register.h updates")'
it is no longer possible to trigger an EMP Reset from debugfs, but it's
possible to request it either way, to end up with a bad reset request:

echo empr > /sys/kernel/debug/i40e/0002\:01\:00.1/command
i40e 0002:01:00.1: debugfs: forcing EMPR
i40e 0002:01:00.1: bad reset request 0x00010000

So let's remove this piece of code and show the available valid commands
as it is when any invalid command is issued.

Signed-off-by: "Mauro S. M. Rodrigues" <maurosr@linux.vnet.ibm.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>