ARM: ixp4xx_defconfig: Cleanup from non-existing options

Remove options which do not exist anymore:
 - ECONET is gone since commit 349f29d8 ("econet: remove ancient bug
   ridden protocol");

 - IPDDP_DECAP is gone since commit 9b5645b5 ("appletalk: remove
   "config IPDDP_DECAP"");
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

arch/arm/configs/ixp4xx_defconfig

@@ -81,12 +81,8 @@ CONFIG_ATALK=m
 CONFIG_DEV_APPLETALK=m
 CONFIG_IPDDP=m
 CONFIG_IPDDP_ENCAP=y
-CONFIG_IPDDP_DECAP=y
 CONFIG_X25=m
 CONFIG_LAPB=m
-CONFIG_ECONET=m
-CONFIG_ECONET_AUNUDP=y
-CONFIG_ECONET_NATIVE=y
 CONFIG_WAN_ROUTER=m
 CONFIG_NET_SCHED=y
 CONFIG_NET_SCH_CBQ=m