aflplusplus: qemu: move to python3

QEMU 3.1 already had support for building with python3, so this should
be a change that doesn't have any effect on the produced binaries.

Python2 removal tracking issue: https://github.com/NixOS/nixpkgs/issues/148779

pkgs/tools/security/aflplusplus/qemu.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchurl, aflplusplus, python2, zlib, pkg-config, glib, perl
+{ lib, stdenv, fetchurl, aflplusplus, python3, zlib, pkg-config, glib, perl
 , texinfo, libuuid, flex, bison, pixman, autoconf
 }:
 
@@ -44,7 +44,7 @@ stdenv.mkDerivation {
   '';
 
   nativeBuildInputs = [
-    python2 perl pkg-config flex bison autoconf texinfo
+    python3 perl pkg-config flex bison autoconf texinfo
   ];
 
   buildInputs = [