A few more process tweaks

- Removes unused btime globals.
- Removes unnecessary multiplication.
- Makes the garbage collector run twice as often, but do half as much
work.
- Makes the garbage collector SCHECK more often when performing hard
deletions.
- Adds a delay to the garbage collector's start.

code/controllers/Processes/garbage.dm

@@ -1,6 +1,7 @@
 /datum/controller/process/garbage_collector/setup()
 	name = "garbage"
-	schedule_interval = 20 // every 2 seconds
+	schedule_interval = 10
+	start_delay = 3
 
 	garbageCollector = src