[TASK] Remove checks for extensions which are always loaded

There are several calls to check if extensions like extbase are loaded.
As those extensions cannot be removed and are always loaded,
the code can be removed.

Resolves: #56858
Releases: 6.2
Change-Id: I434daaa2e5ae98ac623e8c9c06a0cb41560d3610
Reviewed-on: https://review.typo3.org/28335
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Stefan Neufeind
Reviewed-by: Oliver Klee
Tested-by: Stefan Neufeind
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer