Dunking handle_atom_del() in the trash bin. (#77339)

Whatever you do, if it warrants the use of something like
`handle_atom_del`, chances are `Exited` can do it better, as most of
these cases involve movables that shouldn't be moved out of their loc
(`Destroy` forcefully moves movables to nullspace) without calling
specific procs, and for the remaining few, `handle_atom_del` doesn't
even cover the eventuality of a movable being deleted outside the source
atom, so it's quite garbage.

Beside, I feel confident in saying `handle_atom_del()` is older than the
DCS, an echo on the workarounds done at the time.

code/game/objects/items/implants/implantpad.dm

@@ -25,12 +25,12 @@
 		if(case)
 			. += span_warning("There seems to be something inside it, but you can't quite tell what from here...")
 
-/obj/item/implantpad/handle_atom_del(atom/A)
-	if(A == case)
-		case = null
-	update_appearance()
-	updateSelfDialog()
+/obj/item/implantpad/Exited(atom/movable/gone, direction)
 	. = ..()
+	if(gone == case)
+		case = null
+		update_appearance()
+		updateSelfDialog()
 
 /obj/item/implantpad/AltClick(mob/user)
 	..()
@@ -44,7 +44,6 @@
 
 	add_fingerprint(user)
 	case.add_fingerprint(user)
-	case = null
 
 	updateSelfDialog()
 	update_appearance()