[BUGFIX] Wrong note in ResourceFactory

A note in the phpdoc header of ResourceFactory states it is a
lowlevel API. But this is wrong as at least since 6.2 this is
the public API and therefor this note is removed.

Resolves: #56731
Releases: 6.2
Change-Id: I90ed0dafa12656efe6d037abebee7b92de54a6f7
Reviewed-on: https://review.typo3.org/28223
Reviewed-by: Oliver Klee
Reviewed-by: Wouter Wolters
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter