iproute: remove unused patch

In f18efaf26e8, the "patches" attribute was erroneously renamed to
"patch". If you follow the original bug report[1], you'll see that this
has long since been fixed upstream (using a different patch).

1: https://bugs.gentoo.org/show_bug.cgi?id=331447

pkgs/os-specific/linux/iproute/default.nix

@@ -8,8 +8,6 @@ stdenv.mkDerivation rec {
     sha256 = "0vz6m2k6hdrjlg4x0r3cd75lg9ysmndbsp35pm8494zvksc7l1vk";
   };
 
-  patch = [ ./vpnc.patch ];
-
   preConfigure = ''
     patchShebangs ./configure
     sed -e '/ARPDDIR/d' -i Makefile

pkgs/os-specific/linux/iproute/vpnc.patch

@@ -1,15 +0,0 @@
-vpnc fails with "RTNETLINK answers: No such device"
-Patch from: https://bugs.gentoo.org/attachment.cgi?id=245736
-In reference to: https://bugs.gentoo.org/show_bug.cgi?id=331447
-
---- iproute2-2.6.35.old/ip/iproute.c	2010-09-02 16:00:21.805000124 +0200
-+++ iproute2-2.6.35/ip/iproute.c	2010-09-02 16:00:40.782000125 +0200
-@@ -160,7 +160,7 @@
- 	if (r->rtm_family == AF_INET6 && table != RT_TABLE_MAIN)
- 		ip6_multiple_tables = 1;
- 
--	if (filter.cloned == !(r->rtm_flags&RTM_F_CLONED))
-+	if (filter.cloned && !(r->rtm_flags&RTM_F_CLONED))
- 		return 0;
- 
- 	if (r->rtm_family == AF_INET6 && !ip6_multiple_tables) {