[TASK] Fix hardcoded titles in FlexFormContainerContainer

Resolves: #69719
Releases: master
Change-Id: I45528248bf52bf516b925f0dd65deb072f9c3e53
Reviewed-on: http://review.typo3.org/43238


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Tested-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>