Add undelete-frame-max instead of undelete-frame-mode (bug#51883)

Add undelete-frame-max instead of undelete-frame-mode (bug#51883)

* doc/emacs/frames.texi (Frame Commands): Replace
undelete-frame-mode with undelete-frame-max.

* lisp/frame.el (undelete-frame-max): New defcustom, by default 1.
(undelete-frame--handle-delete-frame): Use undelete-frame-max
instead of hard-coded 16.
(undelete-frame-mode): Remove function.
(after-init-hook): Add hook undelete-frame--handle-delete-frame to
delete-frame-functions using after-init-hook to not store the
initial frame.
(undelete-frame): Remove undelete-frame-mode.  Use undelete-frame-max
instead of hard-coded 16.

* lisp/menu-bar.el (menu-bar-file-menu): Remove menu item undelete-frame-mode.

* src/frame.c (Fdelete_frame): Replace `undelete-frame-mode' with
`undelete-frame-max' in the docstring.