[BUGFIX] Change deprecation of DocumentTemplate::sectionEnd

To avoid regressions deprecation logs in core, the deprecation log entry
is only written in 'sectionEnd()' if the sectionFlag is used.

Change-Id: I15330825b2c6455e55ed3f544355b38c47a0929c
Resolves: #72730
Releases: master
Reviewed-on: https://review.typo3.org/45932


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>