/Icon/ Folder cleansing crusade part, I think 4; post-wallening clean-up. (#85823)

Hello everybuddy, your number three rated coder-failure here to clean up
some mess. This PR accomplishes some of the more major structural clean
up changes I wanted to do with /obj/ folder, but decided to wait on
until wallening gets merged, and so, time has come. Several things to
still be done, although I know these cleaning PR's are quite a load, so
will wait for this one to get done with first.

## Why It's Good For The Game
Saner spriters, better sprites, less annoyance. Also deleted a whole
load of redundancy this time around, a lot of sprites which existed
simultaniously in two places now got exit their quantum superposition.

code/game/objects/effects/effect_system/fluid_spread/effects_foam.dm

@@ -291,7 +291,7 @@
 
 /// FOAM STRUCTURE. Formed by metal foams. Dense and opaque, but easy to break
 /obj/structure/foamedmetal
-	icon = 'icons/obj/structures_tall.dmi'
+	icon = 'icons/obj/structures/tall.dmi'
 	icon_state = "metalfoam"
 	density = TRUE
 	opacity = TRUE // changed in New()