[TASK] Remove fallback for not-indexed files

Due to all the refactorings all file-objects are created centralized.
In addition it is not possible anymore to create a file object without
an existing index record. Therefore all the fallback-logic for lazy
loading the index record can be removed from the file object.

In addition the unit tests for these parts of the file object have been
removed, too.

Releases: 6.2
Resolves: #53691
Change-Id: I0a01c12e2caaf8554a5b606b7a85d50b44e0e97c
Reviewed-on: https://review.typo3.org/27193
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack