torsocks: expression cleanups

- Remove redundant preConfigure
  torsocks installs into $libdir/torsocks, so setting libdir=$out/lib
  doesn't really help.  To put the shared objects into $out/lib we'd have
  to manually move them into $out and patch various files (the script
  itself expects $libdir/torsocks).
- Use nativeBuildInputs

pkgs/tools/security/tor/torsocks.nix

@@ -10,10 +10,7 @@ stdenv.mkDerivation rec {
     sha256 = "1xwkmfaxhhnbmvp37agnby1n53hznwhvx0dg1hj35467qfx985zc";
   };
 
-  buildInputs = [ autoreconfHook ];
-  preConfigure = ''
-      export configureFlags="$configureFlags --libdir=$out/lib"
-  '';
+  nativeBuildInputs = [ autoreconfHook ];
 
   patchPhase = ''
     substituteInPlace src/bin/torsocks.in \