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

[Dan Nicolaescu]

The ###autoload in ediff-hook.el is not needed, this file is in the
dumped image, so the autoload's only effect is to make loaddefs.el
bigger and increase the size of the dumped image.

The comment in the file says that the autoload is needed for XEmacs, but
that's not a good reason to keep it in the Emacs CVS, it's a one line
change to a file that almost never changes.

OK to remove the autoload line?