Datum var cleanup (#34314)

* Consolidates datum var location

* Move ui_screen to /datum/tgui

* Move focusers to datum.dm. Move fingerprintslast to /atom

* Remove focusers list, makes mobs check if their focus is QDELETED in Life()

* Consolidate use_tag and var_edited into datum_flags

* Revert garbage comment

* Thought I already removed this

* Remove the var_edited preservation

* Removes focus QDELETED handling

code/datums/datum.dm

@@ -1,14 +1,13 @@
 /datum
-    var/gc_destroyed //Time when this object was destroyed.
-    var/list/active_timers  //for SStimer
-    var/list/datum_components //for /datum/components
-    var/ui_screen = "home"  //for tgui
-    var/use_tag = FALSE
-    var/datum/weakref/weak_reference
+	var/gc_destroyed //Time when this object was destroyed.
+	var/list/active_timers  //for SStimer
+	var/list/datum_components //for /datum/components
+	var/datum_flags = NONE
+	var/datum/weakref/weak_reference
 
 #ifdef TESTING
-    var/running_find_references
-    var/last_find_references = 0
+	var/running_find_references
+	var/last_find_references = 0
 #endif
 
 // Default implementation of clean-up code.
@@ -38,10 +37,4 @@
 			qdel(C, FALSE, TRUE)
 		dc.Cut()
 
-	var/list/focusers = src.focusers
-	if(focusers)
-		for(var/i in 1 to focusers.len)
-			var/mob/M = focusers[i]
-			M.set_focus(M)
-
 	return QDEL_HINT_QUEUE