[BUGFIX] Provide correct description for MAIL settings

Remove old references to SwiftMailer and reference the correct
class/interface names.

Resolves: #95038
Releases: master, 10.4
Change-Id: I4a0f723c36102c61757a7d9ce5bc6c24c88374b5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70824


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Torben Hansen <derhansen@gmail.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>