Documentation: remove nonexistent magic numbers

Documentation: remove nonexistent magic numbers

The entire file blames back to the start of git
(minus whitespace from the RST translation and a typo fix):
  * there are changelog comments for March 1994 through to Linux 2.5.74
  * struct tty_ldisc is two pointers nowadays, so naturally no magic
  * GDA_MAGIC is defined but unused, and it's been this way
    since start-of-git
  * M3_CARD_MAGIC isn't defined, because
    commit d56b9b9c464a ("[PATCH] The scheduled removal of some OSS
    drivers") removed the entire driver in 2006
  * CS_CARD_MAGIC likewise since
    commit b5d425c97f7d ("more scheduled OSS driver removal") in 2007
  * KMALLOC_MAGIC and VMALLOC_MAGIC were removed in
    commit e38e0cfa48ac ("[ALSA] Remove kmalloc wrappers"),
    six months after start of git
  * SLAB_C_MAGIC has never even appeared in git
    (removed in 2.4.0-test3pre6)

magic-number.rst is a low-value historial relic at best and
misleading cruft at worst, so start with cleaning out ones that only
appear therein

Automated:
grep MAGIC Documentation/process/magic-number.rst | while read -r mag _;
do git grep -wF "$mag" | grep -vq '^Documentation.*magic-number.rst:' ||
sed -i "/^$mag/d" \
Documentation/{,translations/{zh_CN,zh_TW,it_IT}/}process/magic-number.rst
done

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Link: https://lore.kernel.org/r/8389a7b85b5c660c6891b1740b5dacc53491a41b.1663280877.git.nabijaczleweli@nabijaczleweli.xyz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>