igb: remove igb_init_managability as it is deprecated

igb_init_managability does not actually perform any function as the two
registers it attempts to write are both read only on the host.  This patch
removes the function and all references to it from the driver.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>