[TASK] Deprecate DocumentTemplate::formWidth()

The method DocumentTemplate::formWidth() is not needed anymore as
the styling can be done by using bootstrap and regular CSS classes.

Resolves: #81540
Releases: master
Change-Id: Id767665e71afc454f04002b6989876ca28354fe3
Reviewed-on: https://review.typo3.org/53185


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>