[TASK] Remove default files (DirectoryIndex)

Few default files are included in the directories typo3 and install
in case the server does not have the necessary DirectoryIndex.

Those can be removed since php is needed and DirectoryIndex
will include index.php in standard setup.

Change-Id: I5b5660b8f74242bd0924c89e105dee6dbb278fb8
Fixes: #45786
Releases: 6.1
Reviewed-on: https://review.typo3.org/18456
Reviewed-by: Wouter Wolters
Reviewed-by: Oliver Klee
Reviewed-by: Soren Malling
Tested-by: Soren Malling
Reviewed-by: Michael Stucki
Tested-by: Michael Stucki