[TASK] Remove superfluous method renderRequestHashField

Method FormViewHelper::renderRequestHashField isn't in use
any more since removing the old Extbase property mapper in
TYPO3 version 6.2. Back then it was forgotten to remove
said superfluous method.

Releases: master
Resolves: #90206
Change-Id: I2f1ae48d182718aef9fb2ae972f9b1d34909e21f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63038


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Susanne Moog <look@susi.dev>