[TASK] Remove deprecated functions from GeneralUtility

getValidClassPrefixes
hasValidClassPrefix

Resolves: #56845
Releases: 6.2
Change-Id: I14ffedbe603a5b5117abfd38b4d25fa12e0cb422
Reviewed-on: https://review.typo3.org/28323
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer