Revert "Overlay/Roundstart fixpack (#24356)"

This reverts commit bf42d769e2.

code/controllers/subsystem/processing/overlays.dm

@@ -18,29 +18,25 @@ var/datum/subsystem/processing/overlays/SSoverlays
 
 /datum/subsystem/processing/overlays/Initialize()
 	initialized = TRUE
-	Flush()
+	for(var/I in processing)
+		var/atom/A = I
+		A.compile_overlays()
+		CHECK_TICK
+	processing.Cut()
 	..()
 
 /datum/subsystem/processing/overlays/Recover()
 	overlay_icon_state_caches = SSoverlays.overlay_icon_state_caches
 	processing = SSoverlays.processing
 
-/datum/subsystem/processing/overlays/fire(resumed = FALSE, mc_check = TRUE)
+/datum/subsystem/processing/overlays/fire()
 	while(processing.len)
 		var/atom/thing = processing[processing.len]
 		processing.len--
 		if(thing)
 			thing.compile_overlays(FALSE)
-		if(mc_check)
-			if(MC_TICK_CHECK)
-				break
-		else
-			CHECK_TICK
-
-/datum/subsystem/processing/overlays/proc/Flush()
-	if(processing.len)
-		testing("Flushing [processing.len] overlays")
-		fire(mc_check = FALSE)	//pair this thread up with the MC to get extra compile time
+		if(MC_TICK_CHECK)
+			break
 
 /atom/proc/compile_overlays()
 	if(LAZYLEN(priority_overlays) && LAZYLEN(our_overlays))