Updates subsystem definitions to new standards. (#17470)

* My heart is dragging me down into...

...oblivion!

* drifting closer to the edge but she won't have me

* ever round me we are dead before we meet her

* for the last time

* wake up in sweat

* n

* fff

* uff

---------

Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/controllers/subsystems/initialization/persistent_configuration.dm

@@ -1,6 +1,4 @@
-/var/datum/controller/subsystem/persistent_configuration/SSpersist_config = null
-
-/datum/controller/subsystem/persistent_configuration
+SUBSYSTEM_DEF(persistent_configuration)
 	name = "Persistent Configuration"
 	init_order = SS_INIT_PERSISTENT_CONFIG
 	flags = SS_NO_FIRE
@@ -17,7 +15,7 @@
 	var/forced_awaymission = FALSE
 
 /datum/controller/subsystem/persistent_configuration/Initialize(timeofday)
-	SSpersist_config = src
+	SSpersistent_configuration = src
 
 	load_from_file("data/persistent_config.json")
 
@@ -25,7 +23,7 @@
 	var/file = file2text(filename)
 
 	if (!file)
-		log_config("SSpersist_config: file [filename] not found, falling back to default values.")
+		log_config("SSpersistent_configuration: file [filename] not found, falling back to default values.")
 		return
 
 	var/list/decoded = null