[BUGFIX] Remove old require_once in index_ts.php

* TimeTracker can be instantiated directly, using autoloader
* Check for loaded ext:cms is obsolete, it is a required extension

Change-Id: Ifd6ab21c7ec3aa1c25c5ef0bf4da8f7a76478a2b
Fixes: #46599
Releases: 6.1
Reviewed-on: https://review.typo3.org/19220
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn