bug#4446: remove ###autoload from ediff-hook.el

[Stefan Monnier]

>> Luckily, ldefs-boot.el saves the day:  Tada!
> Huh, for some reason I thought ldefs-boot wasn't used anymore during
> bootstrap, but it is. I thought this was therefore going to be
> straightforward, but because loadup.el sets purify-flag nil in
> bootstrap-emacs, when the autoloads are made, preloaded-file-list only
> contains loadup.el.

BTW, the list of preloaded files is already encoded in src/Makefile.in.
Or you could otherwise extract it statically with something like

   sed -n -e 's/.*(load "\(.*\)".*/\1/p' lisp/loadup.el


-- Stefan