remove two lines to prevent crash during compile for the mbed frdm k64f

Dependencies:   Socket lwip-eth lwip-sys lwip

Fork of EthernetInterface by mbed official

Revision:
53:318c1a0ad907
Parent:
50:dd8331e55fea
--- a/lwip-sys.lib	Fri Apr 29 01:16:12 2016 +0100
+++ b/lwip-sys.lib	Tue May 10 20:45:40 2016 +0000
@@ -1,1 +1,1 @@
-http://mbed.org/users/mbed_official/code/lwip-sys/#12e78a2462d0
+http://mbed.org/users/mbed_official/code/lwip-sys/#8b8671ab556f