[Staleness] Fix removed object error and clean up (#6241)

* fixing error from plots when removing swg and making methods and props private for swg staleness provider

* removing unsubscribes from destroy hooks if the item has been removed already and reverting an unneccesary change

* checking for undefined staleness response

* removed un-neccesary code

src/plugins/telemetryTable/TelemetryTable.js

@@ -293,6 +293,7 @@ define([
             this.stalenessSubscription[keyString].unsubscribe();
             this.stalenessSubscription[keyString].stalenessUtils.destroy();
             this.handleStaleness(keyString, { isStale: false }, SKIP_CHECK);
+            delete this.stalenessSubscription[keyString];
         }
 
         clearData() {