po: Add a copyright and license notice to the Rules-quot auxiliary files.

po: Add a copyright and license notice to the Rules-quot auxiliary files.

Reported by Joël Krähemann <jkraehemann@gmail.com>
at <https://savannah.gnu.org/bugs/?57973>.

* gettext-runtime/po/quot.sed: Add a copyright and all-permissive license
notice.
* gettext-runtime/po/boldquot.sed: Likewise.
* gettext-runtime/po/en@quot.header: Likewise.
* gettext-runtime/po/en@boldquot.header: Likewise.
* gettext-runtime/po/insert-header.sed: Use an all-permissive license notice.
* gettext-runtime/po/Rules-quot: Likewise.
(.insert-header.po-update-en): After running the *.insert-header script,
eliminate lines that start with %%.