* lisp/emacs-lisp/autoload.el: Improve last change

* lisp/emacs-lisp/autoload.el: Improve last change

It turns out there were other places that used `custom-initialize-delay`
on autoloaded variables and used various hacks to make it work with
`autoload.el`.  The new code makes those hacks unneeded.
Also, there's no point trying to "optimize" those rare cases anyway,
so I simplified the `autoload.el` code for those cases.

(make-autoload): For non-trivial cases,
just include the whole `defcustom` instead of trying to mimic it.

* lisp/mail/rmail.el (rmail-spool-directory): Remove hacks.
* lisp/info.el (Info-default-directory-list): Remove `progn` hack.

* lisp/custom.el (custom-declare-variable)
(custom-handle-all-keywords): Don't use pseudo-group `nil`.