[TASK] Fix comments of DataHandler::clear_cacheCmd()

The doc comments for DataHandler::clear_cacheCmd() contained
outdated information on how to clear the system caches.

Resolves: #91720
Releases: master, 10.4
Change-Id: I42cb2aebecc7ef2eb45b0070e3fff19a199b9651
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64944


Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: TYPO3com <noreply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>