TYPO3 12: CSH is dead

Context sensitive help has been removed for TYPO3 v12:

• https://forge.typo3.org/issues/97312

We shall use the description now, which also works in flexforms:

• TYPO3v10: https://docs.typo3.org/m/typo3/reference-tca/10.4/en-us/Columns/#description