[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
[BUGFIX] Make backend user global available early

The global must be available very early, because methods below
might trigger code which relies on it. In particular the workspace
overlay of the rootline which is done in certain cases.

Fixes: #45625
Releases: 6.0, 6.1
Change-Id: I035f27e11cd56fc284442b66ad8357060f76e52c
Reviewed-on: https://review.typo3.org/18420
Reviewed-by: Mattias Nilsson
Reviewed-by: Oliver Klee
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel
[TASK] Remove not necessary require_once in LiveSearchDataProvider

Change-Id: I2027184626850ff7dc13221b30db9077406ce9ca
Resolves: #45865
Releases: 6.1
Reviewed-on: https://review.typo3.org/18486
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel
Merge remote-tracking branch 'upstream/master'