Demotes the "electrical conductivity" flag from flags_1 to obj_flags (#80033)

## About The Pull Request

Code to handle this flag only ever existed on the `/obj` sublevel, so
there's no need for it to be on the `/atom` level `flags_1`. There was
probably a point in time in which mobs or turfs conducted electricity
but there's zero code for it anymore so we truly just live in a society
now.
## Why It's Good For The Game

Frees up a slot on `flags_1` (which is really nice actually), proper
scoping of certain bitflag stuff, etc.
## Changelog
Not relevant to players.

I may have screwed something up, will be doing a few passes on this
myself to ensure all the search and replaces went alright but we should
be good™️

code/game/objects/structures/cannons/cannonballs.dm

@@ -7,7 +7,7 @@
 	singular_name = "cannonball"
 	merge_type = /obj/item/stack/cannonball
 	throwforce = 10
-	flags_1 = CONDUCT_1
+	obj_flags = CONDUCTS_ELECTRICITY
 	custom_materials = list(/datum/material/alloy/plasteel=SHEET_MATERIAL_AMOUNT)
 	resistance_flags = FIRE_PROOF
 	throw_speed = 5