[TASK] Clarify code comments in GeneralUtility::getUserObj()

The method GeneralUtility::getUserObj() already shows
that it will be exactly the same as makeInstance(), thus it will
be deprecated in TYPO3 v9.0, so the comments can be changed
accordingly already.

Resolves: #78734
Releases: master
Change-Id: I5487e8bc0d1c140110d30098e656f5205750c0f2
Reviewed-on: https://review.typo3.org/50694


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>