delete the re-defined macro

#define RT_LWIP_DNS

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1859 bbd45198-f89e-11dd-88c7-29a3b14d5316

bsp/at91sam9260/rtconfig.h

@@ -163,8 +163,6 @@
 /* Using DHCP */
 /* #define RT_LWIP_DHCP */
 
-#define RT_LWIP_DNS
-
 /* ip address of target */
 #define RT_LWIP_IPADDR0	192
 #define RT_LWIP_IPADDR1	168

bsp/mini2440/rtconfig.h

@@ -151,8 +151,6 @@
 /* Using DHCP */
 /* #define RT_LWIP_DHCP */
 
-#define RT_LWIP_DNS
-
 /* ip address of target */
 #define RT_LWIP_IPADDR0	192
 #define RT_LWIP_IPADDR1	168

bsp/mini4020/rtconfig.h

@@ -133,8 +133,6 @@
 /* Using DHCP */
 /* #define RT_LWIP_DHCP */
 
-#define RT_LWIP_DNS
-
 /* ip address of target */
 #define RT_LWIP_IPADDR0	192
 #define RT_LWIP_IPADDR1	168