Remove support for `editorconfig-exclude-*`

Remove support for `editorconfig-exclude-*`

When using the new hook, we can't support `editorconfig-exclude-modes` for
the `charset` property.  Also there are already other ways to get
similar effects (e.g. setting `auto-coding-alist` or
`enable-dir-local-variables`), so it's not clear those configurations
will be needed in Emacs-30.

* lisp/editorconfig.el (editorconfig-exclude-modes)
(editorconfig-exclude-regexps): Remove custom vars.
(recentf): Remove workaround (presumably not needed thanks to the fix
to issue #246).
(editorconfig--disabled-for-filename)
(editorconfig--disabled-for-majormode): Delete functions.
(editorconfig--advice-find-file-noselect): Remove call to those functions.
(editorconfig-mode): Adjust docstring accordingly.

* lisp/editorconfig-tools.el (editorconfig-apply): Adjust accordingly.

(cherry picked from commit c5d86db81173100bd0303cfb2066b1a0319c2caa)