[TASK] Simplify module menu loading functionality

As there is no relative path functionality but only absolute
URLs (without the domain name but just prepended) the functionality
of stripping the siteUrl is removed, thus allowing to remove the hardcoded
"/typo3/" name in the URL and the siteUrl configuration option as well.

Resolves: #79212
Releases: master
Change-Id: I03a065950bb0401970a618bf30c71d69d6ed2188
Reviewed-on: https://review.typo3.org/51209


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>