[BUGFIX] Install Tool: Remove references to old CSS files

Resolves: #63084
Releases: master
Change-Id: Id261fe8d8e93521f11e33d92e8848d43d0f4d16b
Reviewed-on: http://review.typo3.org/34367
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>