[TASK] Remove all $GLOBALS['rootline'] usages

The getRootline() method of ExtendedTemplateService is broken
because of an incomplete replacement of the web_ts changes.

See https://review.typo3.org/#/c/50626/

The fix replaces the rootline variable in the last occurence
by the correct replacement.

Related: #78675
Resolves: #76545
Releases: master
Change-Id: Ib554679fd86230e183801e9b234a8138d4518cd3
Reviewed-on: https://review.typo3.org/50695


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