[TASK] Load idna_convert via composer

The third-party library is now fetched via composer into typo3/contrib/vendor.

The additional require_once statement in GeneralUtility
is therefore not needed anymore.

Resolves: #65987
Releases: master
Change-Id: Ib7dabba5f7fb697a68ef4178b5ae5f15c56dd4df
Reviewed-on: http://review.typo3.org/38129


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>