keep localStorage tidier

editor/default.ts

@@ -49,13 +49,13 @@ module TDev
 
             if (window.localStorage["lastExceptionMessage"]) {
                 var msg = window.localStorage["lastExceptionMessage"];
-                window.localStorage["lastExceptionMessage"] = "";
+                window.localStorage.removeItem("lastExceptionMessage");
                 if (TDev.Browser.EditorSettings.widgets().notifyAppReloaded)
                     upd = div("app-updated", lf("Something went wrong and we reloaded the app"));
             }
 
             if (!upd && window.localStorage["appUpdated"]) {
-                window.localStorage["appUpdated"] = "";
+                window.localStorage.removeItem("appUpdated");
                 if (dbg)
                     upd = div("app-updated", lf("The TouchDevelop app has been updated."));
             }

editor/scriptList.ts

@@ -260,7 +260,7 @@
                 this.updateIsWaiting = false;
                 tick(Ticks.appUpdate);
                 window.localStorage["appUpdated"] = "1";
-                window.localStorage["lastForcedUpdate"] = "";
+                window.localStorage.removeItem("lastForcedUpdate");
                 window.location.reload();
                 return true;
             }

rt/util.ts

@@ -2650,7 +2650,7 @@ module TDev{
     {
         var b = window.localStorage["storedBug"];
         if (b) {
-            window.localStorage["storedBug"] = "";
+            window.localStorage.removeItem("storedBug");
             try {
                 sendErrorReport(JSON.parse(b));
             } catch (e) {