Save match data in `org-delete-backward-char' and `org-delete-char'

Save match data in `org-delete-backward-char' and `org-delete-char'

* org.el (org-delete-backward-char, org-delete-char): Save
match data (`delete-backward-char' and `delete-char' don't.)
(org-enable-table-editor, org-insert-heading)
(org-remove-timestamp-with-keyword, org-self-insert-command):
Use `delete-backward-char' instead of `backward-delete-char'.

* org-table.el (org-table-fedit-lisp-indent)
(orgtbl-self-insert-command): Ditto.

* org-latex.el (org-export-latex-subcontent): Ditto.

* org-clock.el (org-clocktable-write-default): Ditto.

* org-ascii.el (org-export-ascii-preprocess): Ditto.

Thanks to Vegard Vesterheim for raising this issue and proposing a patch,
and to Carsten for pointing at the root of the problem.