[BUGFIX] Use PHP native htmlspecialchars_decode()

Method Generalutility::htmlspecialchars_decode()
was replaced by htmlspecialchars_decode().
Also  Generalutility::htmlspecialchars_decode()
has been marked as deprecated

Resolves: #54777
Releases: 6.2
Change-Id: Idc9b12d8a1dc2746ee0f742c37c640118c9f69c3
Reviewed-on: https://review.typo3.org/27473
Reviewed-by: Oliver Klee
Reviewed-by: Karol Lamparski
Reviewed-by: Marcin Sągol
Tested-by: Marcin Sągol
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring