remove mention of never used WALL_CLING_FOURTH (#64842)

- introduced in
commit: 2c41bdf
PR: Add ability to count character flags, move all trait flag checks over to character flag (#55061)

doc/JSON_FLAGS.md

@@ -490,7 +490,6 @@ Some armor flags, such as `WATCH` and `ALARMCLOCK` are compatible with other ite
 - ```WEBBED_HANDS``` You have webbings on your hands, supporting your swimming speed.
 - ```WEB_RAPPEL``` You can rappel down staircases and sheer drops of any height.
 - ```WALL_CLING``` You can ascend/descend sheer cliffs as long as the tile above borders at least one wall. Chance to slip and fall each step.
-- ```WALL_CLING_FOURTH``` Same as `WALL_CLING`, but you need four instances of the flag for it to function (ex. four bodyparts with the flag).
 - ```WINGS_1``` You have 50% chance to ignore falling traps (including ledges).
 - ```WINGS_2``` You have 100% chance to ignore falling traps (including ledges).  Requires two flag instances.