[BUGFIX] LocalizationUtility methods should be static

All public methods of LocalizationUtility are static, but two
protected methods are not. Make those static, too.

Change-Id: I267805cad3f008f24e053f69670fac0f805f7ad2
Resolves: #58600
Releases: 6.2
Reviewed-on: https://review.typo3.org/29921
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Markus Klein
Tested-by: Markus Klein