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/processing/nanoui.dm

@@ -1,6 +1,4 @@
-var/datum/controller/subsystem/processing/nanoui/SSnanoui
-
-/datum/controller/subsystem/processing/nanoui
+PROCESSING_SUBSYSTEM_DEF(nanoui)
 	// Subsystem stuff.
 	name = "NanoUI"
 	flags = SS_NO_INIT
@@ -10,9 +8,6 @@ var/datum/controller/subsystem/processing/nanoui/SSnanoui
 	// NanoUI stuff.
 	var/list/open_uis = list()
 
-/datum/controller/subsystem/processing/nanoui/New()
-	NEW_SS_GLOBAL(SSnanoui)
-
  /**
   * Get an open /nanoui ui for the current user, src_object and ui_key and try to update it with data
   *