[IRDA]: Remove irlan_eth_send_gratuitous_arp()

Even kernel 2.2.26 (sic) already contains the
  #undef CONFIG_IRLAN_SEND_GRATUITOUS_ARP
with the comment "but for some reason the machine crashes if you use DHCP".

Either someone finally looks into this or it's simply time to remove
this dead code.

Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>