[!!!][TASK] Have ResourceCompressor calculate relative paths

The Resource Compressor component does not use the
PathUtility API to calculate the back paths to the current
script but handles it with a custom variable based on the
TYPO3_MODE which is not needed anymore.

The code can thus be simplified.

Resolves: #73611
Releases: master
Change-Id: If72f3ef4b385c253e610c11ea920cc1fab48edff
Reviewed-on: https://review.typo3.org/46821


Reviewed-by: Sebastian Fischer <typo3@evoweb.de>
Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Daniel Gorges <daniel.gorges@b13.de>
Tested-by: Daniel Gorges <daniel.gorges@b13.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>