[BUGFIX] Flexform element title is cropped to hardcoded length

The title of a flexform element is cropped to maximum length of 30
characters. Instead it should obey the maximum title length in the user
settings.

Resolves: #58910
Releases: 6.2, 6.1
Change-Id: I28c6fc94b2d492217479bf014ff8f67463b4e98f
Reviewed-on: https://review.typo3.org/30242
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters