ui: the ui-thread variable isn't needed

basis/ui/ui.factor

@@ -132,8 +132,6 @@ M: world ungraft*
     redraw-worlds
     send-queued-gestures ;
 
-SYMBOL: ui-thread
-
 : ui-running ( quot -- )
     t \ ui-running set-global
     [ f \ ui-running set-global ] [ ] cleanup ; inline
@@ -155,7 +153,7 @@ PRIVATE>
     ! run one iteration of update-ui. If that also fails, well, the
     ! whole UI subsystem is broken so we throw the error to terminate
     ! the update-ui-loop.
-    [ { [ ui-running? ] [ ui-thread get-global self eq? ] } 0&& ]
+    [ ui-running? ]
     [
         ui-notify-flag get lower-flag
         [ update-ui ] [
@@ -166,8 +164,7 @@ PRIVATE>
     ] while ;
 
 : start-ui-thread ( -- )
-    [ self ui-thread set-global update-ui-loop ]
-    "UI update" spawn drop ;
+    [ update-ui-loop ] "UI update" spawn drop ;
 
 : start-ui ( quot -- )
     call( -- ) notify-ui-thread start-ui-thread ;