Use new `derived-mode-all/set-parents` functions.

Use new `derived-mode-all/set-parents` functions.

Try and avoid using the `derived-mode-parent` property directly
and use the new API functions instead.

* lisp/emacs-lisp/derived.el (define-derived-mode):
Use `derived-mode-set-parent`.

* lisp/loadhist.el (unload--set-major-mode):
* lisp/info-look.el (info-lookup-select-mode):
* lisp/ibuf-ext.el (ibuffer-list-buffer-modes):
* lisp/files.el (dir-locals--get-sort-score):
* lisp/emacs-lisp/cl-generic.el (cl--generic-derived-specializers):
Use `derived-mode-all-parents`.