Docs: remove reference to PYTHONHOME

This is no longer used by default, when '--python-use-system-env' is set
there are many Python environment variables, don't list them in
Blender's help message.

source/creator/creator_args.c

@@ -683,7 +683,6 @@ static int arg_handle_print_help(int UNUSED(argc), const char **UNUSED(argv), vo
 #  ifdef WITH_SDL
   printf("  $SDL_AUDIODRIVER          LibSDL audio driver - alsa, esd, dma.\n");
 #  endif
-  printf("  $PYTHONHOME               Path to the Python directory, eg. /usr/lib/python.\n\n");
 
   exit(0);