[!!!][TASK] Remove TBE_EDITOR.fieldChanged_fName

The JavaScript functions TBE_EDITOR.fieldChanged_fName` and its legacy
alias `TBE_EDITOR_fieldChanged_fName` used to extract the table name,
field name and uid from the incoming field name have been removed.

As a drive-by bugfix, the undefined variables
`TBE_EDITOR_setHiddenContent` and `TBE_EDITOR.setHiddenContent` have
been removed as well.

Resolves: #91578
Releases: master
Change-Id: I528fde709367d5d474b846f347a3770d15b1a227
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64678


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>