[TASK] ResourceStorage: Remove getFileInfoByIdentifier() method

The method getFileInfoByIdentifier() has been marked as deprecated long
ago. Additionally, the getFileInfo() method currently uses incorrect
semantics - it expects an identifier, while it should use a file object
to be in line with all other public FAL API methods.

Change-Id: Id76c1a03dcbcead33a16c6410ad93c66dafaa5c6
Resolves: #40520
Releases: 6.0
Reviewed-on: http://review.typo3.org/14281
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter
Reviewed-by: Mario Rimann
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack