[TASK] Simplify newly created base of a site language

If a new site is created from the Install Tool, the base of the default
language should be changed from '/en/' to '/' to have a shorter url.

Resolves: #90718
Releases: master
Change-Id: Ied58d18136b0e587588425bf119c0e4573836690
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63650


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Christian Eßl <indy.essl@gmail.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Josef Glatz <josefglatz@gmail.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Christian Eßl <indy.essl@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Josef Glatz <josefglatz@gmail.com>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>