[!!!][TASK] Remove CSP violating BU::getFuncInput()

BackendUtility::getFuncInput() is a (core) unused
utility method that violates Content-Security-Policy
headers due to onclick attribute. It is of very
limited help anyways and should be removed.

Resolves: #96829
Releases: main
Change-Id: I371a5eb922c4c4b28bc67fc67e2293fe19988d15
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73424


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Bartsch <bo@cedev.de>