mdadm: use shared system-sendmail

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

@@ -1,18 +1,5 @@
-{ stdenv, writeScript
-, fetchurl, groff
-}:
-
-let
-  sendmail-script = writeScript "sendmail-script" ''
-    #!/bin/sh
-
-    if [ -x /run/wrappers/bin/sendmail ]; then
-      /run/wrappers/bin/sendmail "$@"
-    else
-      /run/current-system/sw/bin/sendmail "$@"
-    fi
-  '';
-in
+{ stdenv, writeScript, fetchurl, groff, system-sendmail }:
+
 stdenv.mkDerivation rec {
   name = "mdadm-4.1";
 
@@ -23,7 +10,7 @@ stdenv.mkDerivation rec {
 
   # This is to avoid self-references, which causes the initrd to explode
   # in size and in turn prevents mdraid systems from booting.
-  allowedReferences = [ stdenv.cc.libc.out sendmail-script ];
+  allowedReferences = [ stdenv.cc.libc.out system-sendmail ];
 
   patches = [ ./no-self-references.patch ];
 
@@ -40,7 +27,7 @@ stdenv.mkDerivation rec {
   preConfigure = ''
     sed -e 's@/lib/udev@''${out}/lib/udev@' \
         -e 's@ -Werror @ @' \
-        -e 's@/usr/sbin/sendmail@${sendmail-script}@' -i Makefile
+        -e 's@/usr/sbin/sendmail@${system-sendmail}@' -i Makefile
   '';
 
   meta = with stdenv.lib; {