[BUGFIX] Fix links to backend admin / frontend website in Install Tool

The install tool (/typo3/install.php) is at the same directory location
as the backend interface. The links are fixed to point to the correct
locations.
Remove an obsolete f:if along the way, this partial is only loaded
in non backend context anyway.

Resolves: #82199
Related: #76084
Releases: master
Change-Id: I73ff8b0a3bd22827fa2a2c319b0e0bb2ad4e5afa
Reviewed-on: https://review.typo3.org/53803


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: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>