[TASK] Remove creation of _cli_scheduler in BE

The _cli_scheduler backend user was necessary before the
introduction of the unified "_cli_" user for all CLI processes.

The scheduler module had an info and functionality to
create such a user which is not needed anymore and
can safely be removed.

Resolves: #79264
Releases: master
Change-Id: Ie2472869b9db1fc9dcb4add9fae6be63722156c6
Reviewed-on: https://review.typo3.org/51256


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>