ui.backend.cocoa: simplify system-alert implementation now that callbacks bug has been fixed

basis/ui/backend/cocoa/cocoa.factor

@@ -217,7 +217,6 @@ M: cocoa-ui-backend beep ( -- )
     NSBeep ;
 
 M: cocoa-ui-backend system-alert
-    invalidate-run-loop-timers
     NSAlert -> alloc -> init -> autorelease [
         {
             [ swap <NSString> -> setInformativeText: ]
@@ -225,8 +224,7 @@ M: cocoa-ui-backend system-alert
             [ "OK" <NSString> -> addButtonWithTitle: drop ]
             [ -> runModal drop ]
         } cleave
-    ] [ 2drop ] if*
-    init-thread-timer ;
+    ] [ 2drop ] if* ;
 
 CLASS: FactorApplicationDelegate < NSObject
 [