[BUGFIX] Aboutmodules: Removed call to deprecated method render()

The call of FlashMessage->render() is removed and the message output
is done using the InfoboxViewhelper now.

Resolves: #72442
Releases: master, 7.6
Change-Id: Id4017e1b645917827d71dab76f74b0bd4eed94a8
Reviewed-on: https://review.typo3.org/45442


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>