Fix generate.py script for Python 3.12.

It now no longer works with Python <3.2.

utils/multires/generate.py

@@ -1,12 +1,12 @@
 #!/usr/bin/env python3
 
-# Requires Python 3.2+, the Python Pillow and NumPy packages, and
+# Requires Python 3.3+, the Python Pillow and NumPy packages, and
 # nona (from Hugin). The Python pyshtools package is also needed for creating
 # spherical-harmonic-transform previews (which are recommended).
 
 # generate.py - A multires tile set generator for Pannellum
 # Extensions to cylindrical input and partial panoramas by David von Oheimb
-# Copyright (c) 2014-2022 Matthew Petroff
+# Copyright (c) 2014-2023 Matthew Petroff
 # 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -34,7 +34,7 @@ import os
 import sys
 import math
 import ast
-from distutils.spawn import find_executable
+from shutil import which as find_executable
 import subprocess
 import base64
 import io