[TASK] Deprecate GeneralUtility::stdAuthCode

GeneralUtility::stdAuthCode is unused since at least
v9. As more appropriate methods for generating hashes,
e.g. GeneralUtility::hmac() exists nowadays, the method
is deprecated.

Resolves: #94309
Releases: master
Change-Id: I3d3678cd8c8c76462cc74b28f629b6679a4aea93
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/69458


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Torben Hansen <derhansen@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>