i40e: drop unused function

Delete the unused irq_dynamic_disable function.

Change-ID: Ia46071066babd121c7c90f141b6210b00078de3f
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Reviewed-by: Anjali Singhai <anjali.singhai@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>