[!!!][TASK] Remove backPath from PageRenderer

The backPath option in page renderer can be removed
and adding the necessary path for the libraries is now done
with a simple condition to resolve the path to the files.

Resolves: #73763
Releases: master
Change-Id: I917c4310834628427a53d248f8a6be3830c3bd91
Reviewed-on: https://review.typo3.org/46971


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>