rsnapshot: Remove unnecessary argument, refactor one-line patch to flags.

pkgs/tools/backup/rsnapshot/default.nix

···
-{ fetchurl, stdenv, writeText, perl, openssh, rsync, logger,
-  configFile ? "/etc/rsnapshot.conf" }:
+{ fetchurl, stdenv, writeText, perl, openssh, rsync, logger }:
 
-let patch = writeText "rsnapshot-config.patch" ''
---- rsnapshot-program.pl	2013-10-05 20:31:08.715991442 +0200
-+++ rsnapshot-program.pl	2013-10-05 20:31:42.496193633 +0200
-@@ -383,7 +383,7 @@
- 	}
- 	
- 	# set global variable
--	$config_file = $default_config_file;
-+	$config_file = '${configFile}';
- }
- 
- # accepts no args
-'';
-in
 stdenv.mkDerivation rec {
   name = "rsnapshot-1.4.1";
 
···
 
   propagatedBuildInputs = [perl openssh rsync logger];
 
+  configureFlags = [ "--sysconfdir=/etc --prefix=/" ];
+  makeFlags = [ "DESTDIR=$(out)" ];
+
   patchPhase = ''
     substituteInPlace "Makefile.in" --replace \
       "/usr/bin/pod2man" "${perl}/bin/pod2man"
-    patch -p0 <${patch}
   '';
 
   meta = with stdenv.lib; {