Documentation: HFS is not a user of magic numbers

In fs/hfs, the only magic is for delineating on-disk block types,
of which HFS_DRVR_DESC_MAGIC HFS_MFS_SUPER_MAGIC are define-only,
but they're out of scope for magic-number.rst

Magic numbers as described there were all removed, along their defines,
in the 2.6.4 "HFS rewrite", pre-git

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Link: https://lore.kernel.org/r/e67cec702a7ab34a8c5f7966d930d793a097a90f.1663280877.git.nabijaczleweli@nabijaczleweli.xyz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>