[TASK] Deprecate GeneralUtility::getUserObj()

This function now does the same as makeInstance() except for an if()
clause, since the API should be unified this method should be considered
as dropped, allowing to use callUserFunction() and makeInstance() as the
only two proper ways to call custom classes / methods.

Resolves: #80993
Releases: master
Change-Id: I0c2042dbe6c83a86f211bab4eaf64d75e6424232
Reviewed-on: https://review.typo3.org/52518


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>