[TASK] Use TYPO3_OS constant in Services registration

There is a comment that TYPO3_OS is not yet defined, which
is wrong as it is one of the first things available during bootstrap,
so the check can be used directly.

Resolves: #82343
Releases: master, 8.7
Change-Id: I01e0aa7a090bc068195b44474f645d09220f8b71
Reviewed-on: https://review.typo3.org/53953


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>