mail/datovka: update to 4.24.0

Fix LICENSE.
Add STRIP_CMD to post-install.
Add USES=compiler:c++11-lang.
Improve pkg-descr.

Changelog: https://www.datovka.cz/cs/2024-06-18-datovka-4.24.0.html

PR: 279400
Approved by: submitter is maintainer