Remove clone-number support. Provide clone-of parameter in window states.

Remove clone-number support.  Provide clone-of parameter in window states.

* window.h (window): Remove clone_number slot.
* window.c (Fwindow_clone_number, Fset_window_clone_number):
Remove.
(make_parent_window, make_window, saved_window)
(Fset_window_configuration, save_window_save): Don't deal with
clone numbers.
* buffer.c (Qclone_number): Remove declaration.
(sort_overlays, overlay_strings): Don't deal with clone numbers.

* window.el (window-state-get-1): Don't assign clone numbers.
Add clone-of item to list of window parameters.
(window-state-put-2): Don't process clone numbers.
(display-buffer-alist): Fix doc-string.