openvpn: remove no longer correct systemd-notify.patch

This patch was only necessary for 2.3.x, while 2.4.0 improved
its own systemd notify support.

See: https://github.com/NixOS/nixpkgs/issues/24817

pkgs/tools/networking/openvpn/default.nix

@@ -15,8 +15,6 @@ stdenv.mkDerivation rec {
     sha256 = "0zpqnbhjaifdalyxwmvk5kcyd7cpxbcigbn7967nbsyvl54vl8vg";
   };
 
-  patches = optional stdenv.isLinux ./systemd-notify.patch;
-
   buildInputs = [ lzo openssl pkgconfig ]
                   ++ optionals stdenv.isLinux [ pam systemd iproute ]
                   ++ optional pkcs11Support pkcs11helper;

pkgs/tools/networking/openvpn/systemd-notify.patch

@@ -1,22 +0,0 @@
-diff -ru -x '*~' openvpn-2.3.1-orig/src/openvpn/init.c openvpn-2.3.1/src/openvpn/init.c
---- openvpn-2.3.1-orig/src/openvpn/init.c	2013-03-20 09:28:14.000000000 +0100
-+++ openvpn-2.3.1/src/openvpn/init.c	2014-04-22 13:02:21.351026640 +0200
-@@ -48,6 +48,8 @@
- 
- #include "occ-inline.h"
- 
-+#include <systemd/sd-daemon.h>
-+
- static struct context *static_context; /* GLOBAL */
- 
- /*
-@@ -1375,6 +1375,9 @@
-     /* Reset the unsuccessful connection counter on complete initialisation */
-     c->options.unsuccessful_attempts = 0;
- 
-+    /* Tell systemd we're ready. */
-+    sd_notify(0, "READY=1");
-+
-     /* If we delayed UID/GID downgrade or chroot, do it now */
-     do_uid_gid_chroot (c, true);
-