Use delete-selection-mode in cua-mode.

Use delete-selection-mode in cua-mode.
* lisp/emulation/cua-base.el (cua--prefix-copy-handler)
(cua--prefix-cut-handler): Rely on region-extract-function rather than
checking cua--rectangle.
(cua-delete-region): Use region-extract-function.
(cua-replace-region): Delete function.
(cua-copy-region, cua-cut-region): Obey region-extract-function.
(cua--pre-command-handler-1): Don't do the delete-selection thing.
(cua--self-insert-char-p): Ignore `self-insert-iso'.
(cua--init-keymaps): Don't remap delete-selection commands.
(cua-mode): Use delete-selection-mode instead of rolling our own.
* lisp/emulation/cua-rect.el (cua--rectangle-region-extract): New function.
(region-extract-function): Use it.
(cua-mouse-save-then-kill-rectangle): Use cua-copy-region.
(cua-copy-rectangle, cua-cut-rectangle, cua-delete-rectangle):
Delete functions.
(cua--init-rectangles): Don't re-remap copy-region-as-kill,
kill-ring-save, kill-region, delete-char, delete-forward-char.
Ignore self-insert-iso.
* lisp/menu-bar.el (clipboard-kill-ring-save, clipboard-kill-region):
Obey region-extract-function.
* lisp/emulation/cua-gmrk.el (cua--init-global-mark):
Ignore `self-insert-iso'.

Fixes: debbugs:16085