iproute2: drop unneeded Werror handling

Upstream has dropped -Werror since the 3.12 release, so there's no point in
us sed'ing it away:

https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/commit/?id=3140e9a3a343d37a8d828ee27e16ad9f3f9ab389

Reported-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/iproute2/iproute2.mk

@@ -51,7 +51,6 @@ endif
 define IPROUTE2_CONFIGURE_CMDS
 	$(SED) 's/gcc/$$CC $$CFLAGS/g' $(@D)/configure
 	cd $(@D) && $(TARGET_CONFIGURE_OPTS) ./configure
-	$(SED) 's/-Werror//' $(IPROUTE2_DIR)/Makefile
 	$(IPROUTE2_DISABLE_ARPD)
 	$(IPROUTE2_WITH_IPTABLES)
 endef