[TASK] Remove "hreflang" from site configuration

With the introduction of the Locale API in 12.2
and its inclusion in SiteLanguage->getLocale(),
the property "hreflang" can be completely removed
from the Site Configuration, as the Locale API can
 convert the hreflang property properly into
a format like "de-AT" directly.

This format is described as IETF RFC 5646 language
tag standard: https://www.rfc-editor.org/rfc/rfc5646.html

Resolves: #99908
Releases: main
Change-Id: Ie712a89b41e5f00d1c592fc3cc978f58712ef0c4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77807


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>