[TASK] Cleanup ext:setup and ext:tstemplate

* Remove require_once calls
* Move language inclusion to init() for ext:setup

Change-Id: Icdb07a7170e40d57a93fcdc69e788081a47cac6c
Resolves: #49580
Releases: 6.2
Reviewed-on: https://review.typo3.org/21791
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
[BUGFIX] EM: Scheduler task does not persist to database

The scheduler task for updating extension list of the extension
manager does not persist his data to database. As Scheduler is no
extbase extension and the task is no extbase task this peristence
isn't called at end of script.

Change-Id: I75629874f698f45f1b7dab47636857b5865e8d24
Resolves: #49528
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/21760
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring