[BUGFIX] Output correct max upload size

We should show what the max upload file size is and not the max size of
a HTTP post body.

Resolves: #83230
Releases: master, 8.7, 7.6
Change-Id: Ib6fa244b19c434417808bb19126f862cf9418fb0
Reviewed-on: https://review.typo3.org/54937


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>